making UI strings configurable / providing alternative icons

[cmtt]

This could be useful for i18n purposes.

[OscarGodson]

Great idea! Anyway you can submit this without all the whitespace changes? :)

[cmtt]

In addition, this pull request includes now alternative hand-drawn icons.

[OscarGodson]

Hey @cmtt - I want you to be able to be listed as a contributor on the https://github.com/OscarGodson/EpicEditor/graphs/contributors page, but right now there's a bunch of other commits. The sketch icons are nice but those would be part of a theme or something, not the core plus I dont want this package to grow too large. If you want to be listed there could you post a new pull request with just your UI string commit and without the whitespace changes?

If you don't care I'll just make the change.

[cmtt]

This is surely reasonable, I should have had committed the icons in a seperate pull request.
Eventually, the original changes are re-submitted in #199 .