Webscrapbook

* Adjusted filename tidying strategy:
* Spaces, tabs, and linefeeds are now collapsed into a space.
* "~", "<", and ">" are now translated into "_".
* Fixed an error when downloading a file like " .ext".
* Fixed an error when downloading a file with certain Unicode chars like U+00A0 or U+00AD in some browsers.
* Fixed an error when downloading a file with Windows preserved filename like "CON" and "NUL.txt".
* Added support for pinning editor toolbar to the top (through a command in the `Save` dropdown).

* Fixed encoding error when viewing a MAFF/HTZ document with non-UTF-8 encoding.

* Fixed a potential error that a capture hangs during downloading.
* Improved some tooltips.

* Fixed an error when the downloaded folder name happens to contain bad ending chars after cropping.
* Fixed infinite loop when the downloaded folder cannot be generated.
* Fixed missing error message when an error occurs during folder name determination.

* Fixed an issue that the "attrs" property is ignored when the "value" property is set for the "insert" command of a capture helper.

* Added support of more URL placeholders for `capture.saveFilename` option.
* Improved some tooltips.