All features in one release (mouse, locales, ...)

This release contains the following pull request merged together:

• KeyCapBorder-for-all-special-keys
• better-repeat-logic-for-letters (allows ... and billy)
• hide-overlay-window
• locale-keyboard-support
• mouse-click-highlight (v2 with cursor highlight and mouse clicks shown as keys with a symbol)
• show-all-modifiers (toggle if show only modifers shortucs or all keys)
• show-modifier-keys-while-down (holding down a modifier key without shortcut will show it until a key is pressed)

There are lots of features interacting together therefore there might be bugs in some edge cases, please provide bug reports.