Nautilus-terminal

* Improve packageability (63)
* Adds some documentation for packagers

* Install and compile GLib schema on user-install
* Update the documentation

* Nautilus 40 support
* New logo
* Adds an "About" window
* Adds a context menu to copy/paste, run dconf-editor and display the "About" window
* Adds a CLI to check, install, uninstall, print debug,... (`nautilus-terminal -h`)
* Fixes Nautilus Terminal stealing the focus in new Nautilus windows (tkachen, 54)
* Adds an option to clear the terminal after each navigation (tkachen, 55)

**WARNING:** This will be the last version to support Python 2.7!

* Fixes minimum height when the teminal is on the bottom (tkachen, 52)
* Allows to configure the font (tkachen, 10, 53)
* Drops Python 3.6 support
* Coding style enforced using Black

* Allows to configure the terminal toggle shortcut (50, 43)
* Allows to configure terminal background and text color (32)