Add feature to allow user to select number of spaces/tabs.

[joekamien]

Previously, two spaces were always used for indentation.
This change allows the user to select any number from 0-100 and allows the user to select tabs instead of spaces.

[joekamien]

This should address issue #11.

[dimitrisnl]

Hey @joekamien , thanks for helping out!

1. I like the feature. I was thinking of remaking the whole 'actions' bar, and I believe that with the inclusion of this feature, now it's the time.

2. Actually, the Keyframes indentation needs more space #11 issue just mandates a bit more indentation, since the @Keyframes declaration has nested stuff.

I'll hold on this until I get some styling work done.