Fix intermap teleports for maps

Original author: Igor Paliychuk
Remove obsolete key "allow_power_mod" from powers/powers.txt
Convert frame durations to ms
Add background to power tree

This fixes the powers not being visible, but this is a bug and we should
not require a background image to render powers icons.
Merge pull request #72 from dorkster/feature/engine_0.19

Feature/engine 0.19