Add support for deleting colour schemes

This adds two new commands that allow the existing colour scheme
to be deleted after switching to the next/previous scheme. Only
tested on OSX, so may or may not work on other OSes.
Add menu to Package Preferences for keybindings

Duplicated the default keymap to create 3 system-specific versions,
and added a menu to Package Settings so they can be easily accessed
and changed by the user.
Update keybindings

When using PC keyboards on OSX, the function keys aren't always usable
(for example, when using software to remap them to the normal OSX
"special" keys such as Mission Control, Play/Pause etc). This changes
the default keybindings to use page up/down which, I think, makes more
sense. Also adds new keybindings for the delete commands added previously.

Spring cleaning

Changes confirmation messages to use friendly filename (ie without
the file extension) but other than that this is mostly just moving
stuff around. Ignore this commit, basically.
Update readme
Merge branch 'feature/scheme-deletion' into develop
Readme fixes
Rename files for name change
Change package name across the board
Merge branch 'release/0.1'