Show Kodable logo in About dialog
Tweaked hardcoded properties

* Hardcoded properties renamed and now update correctly
* Custom property editing has been disabled
* Looper property now set to empty string instead of 'true'
Use 33% as default zoom for map and tileset views

Also implemented a size hint on the tileset dock to make it have a nicer
default size.
Added a quick note about Kodable to the README.md
Removed add/remove properties button from Properties dock

Shouldn't be allowed to add/remove custom properties in this version.