Fixed a bug with some hotkey texts appearing...

...when hotkeys.xml was not defined yet
Source: newly created Hotkey classes were enabled by default, fix is to
just disable relevant hotkeys in Manager#loadDefaultHotkeys
Formatted up Hotkey#toString
Refactored the event system somewhat...

...type replaced by subclasses,
Added a missing hotkey hook for Mac Command modifier (though it
shouldn't affect anything, since it wasn't used)
Tweaked tooltips to appear 5px lower
Added 'Follow Hull' button to Mount Tool
Improved stats display in weapon/drone selection
Minor UI tweaks
Update changelog.txt