Simple-editor

* Fix for linenumbers missing if closing and re-opening editor in same python-console -session.
* Removed borders from text-widgets, so focus-changes no more messes them up.
* Comment shortcut changed from Control-C to Shift-Return
* Uncomment shortcut changed from Control-X to Shift-BackSpace
* In error-view: files that are in openfiles are now in red color for easier spotting from messy traceback
* So there was this nasty bug if closing editor while in error-view or help-view, contents of current tab, if it had filepath, would be overwritten with error-messages or help-text. It is fixed. Yes, it was quite a bad one. Keep those commits short.
* Disabled copying linenumbers and hided selection of linenumbers
* Git branch, if on one, is now shown next to filepath.

* Migrated from pkg_resources to importlib.resources
* Configuration is now saved as relative to environment in which python-console
was launched. If you have two different python-venvs in same folder, they
will have separate configs. This is why sys is now imported, to get
sys.prefix and compare it to sys.base_prefix. Conf-file, editor.cnf is now
in root of sys.prefix and is _not_ saved if not in virtual environment.

When earlier conf was moved to package dir, it caused an issue: conf was not
removed when pip uninstall, because it was put there after install and so
pip does not recognise it as part of package.

I first thought about system-wide approach and use platformdirs to save conf
in users .config-folder but I could not get OS-pip to:

console
foobar:~$ OS-pip install myprog
foobar:~$ cd myproject
foobar:~/myproject$ source myenv/bin/activate
(myenv) foobar:~/myproject$ python
------------------------------------
>>> import myprog


It would not import it. I now found this pyvenv.cfg -file which is in root of myvenv
and it has this line: include-system-site-packages = false , so maybe this was the cause,
but it is what it is now, I might try it again later.

* Removed indent and unindent from popup as impractical.
* Made unindent to place cursor the same way as indent.
* Hitting just Enter or putting -1 in gotoline moves cursor to file-end.
* Updated help and other small fixes.

* Added initial line numbering. I could not have get it right without
this great [example](https://www.daniweb.com/posts/jump/1246804).
I fixed the offset of lines and choosed not to use after_idle even
that it would be smoother but would also use about double cpu
compared to after 100ms. I also left placeholder for menu-button.

* Some fixes to gotoline.
* Removed reference to '/' at first conf-saving.
* When doing multiline pasting, new content gets now selected
to make it more easy to indent. Press arrow left after block is
in right position to get started indenting first line if necessary.

* Removed not needed import of module os
* Fix for oldcontents showing in conf-file
* Conf-file moved to package dir
* Added check for font-existence
* It is now possible to open and save all text-files, like md and txt etc.
* Ctrl-n now binded to contents instead of root, reason:
if new_tab(): old tabs cursor position would move down one line.
It is possibly a Text-widget -behaviour.

* Widget-packing with grid() instead of pack()
* Fix for not being able to config scrollbar slider size
* Fix for crash when searching etc. in tab without filepath
* Now check of file-changes is always made before writing anything to disk