gd: fixed some typos
Merge pull request #939 from gunchleoc/master

gd: fixed some typos
Simplify duplicate code in ModManager
Add mod descriptions

Closes #542

Descriptions are place in mods/$MOD/settings.txt like so:

description=This is a description

They are displayed as tooltips in the mod list boxes on the
Configuration screen.
Add support for mod dependencies

Closes #733

In mods/$MOD/settings.txt, use:

requires=mod1,mod2,etc

If there's a missing dependency, the game will search all available mods
for it. If it still can't find it, the mod that requires the missing mod
will be disabled. applyDepends() will run recursivly until all
dependencies are met and in the correct order.
Add dependency list to mod tooltips
Clarify which mod is being enabled/disabled in console messages
Fix blank mod tooltips
Merge pull request #941 from dorkster/mods

ModManager improvments
Don't free Image surfaces when copying/destroying Sprite objects

This fixes some bugs where surfaces were getting freed early due to STL
container operations. This let's free Sprite graphics when (and only when)
we are done with them. This is how we originally did things; it's just
abstracted through RenderDevice now.

Also in this commit, I have moved the loading of the icons Sprite to
createContext(), similar to what was done in the SDL2 port.
Merge pull request #942 from dorkster/sprite_refactor

Don't free Image surfaces when copying/destroying Sprite objects
Merge branch 'master' into sdl2

Conflicts:
	src/GameStateConfig.cpp
Don't destroy SDL2 Texture in Sprite operators

Like SDL1, only do this in Sprite::clearGraphics().