* Removes support for Firefox versions 52-61
* improve settings page
* exclude hidden tabs by default

* improve canvas font drawing code
* improve reloading for some option changes

* add font selection popup
* add support for displaying both per window and global tab counts in icon
* apply new settings immediately instead of reloading whole extension
* requires Firefox 59+ in some cases, falling back on reload otherwise
* increase default icon size to 32px
* fix tab counts being off when closing multiple tabs at once on some Firefox versions

Smoother tab transitions in Firefox 62 and upwards

Fixed a bug where saving options failed because of the reload immediately afterwards.
The 'reload' button (old 'save') still tries to save, but in case it doesn't work there's a seperate 'save' button now that does not reload.

* default to 16 CSS px for icon
* improved text placement

* add ability to change font size

* fix icon (canvas) text drawing