More fonts, custom fonts, more transitions

Pocket platformer now has more selectable fonts. They are common fonts which should be available on all OS. 

It is also possible to add a custom font from google.
To do this, go to https://fonts.google.com/, and copy the name of a font you like.

F.e.:

There is also a preview canvas, if you want to have a look at the transition before adding it to your game.

Some other small improvements:

• The UI of the background image selection was simplified
• The dialogue text always looks the same, despite zoom factor and some other visual polishing
• The dialogue sound plays continously, until the whole text is displayed
• The tool doesn't break if a controller is connected, which the tool doesn't support