Allow translating default hero names

Also, I moved the newline outside of the "Next Level:" string in Power
tooltips. This is because it messed up po/pot generation.
Merge pull request #910 from dorkster/fixes

Allow translating default hero names
Rendering refactor:
* Move API related code to SDLRenderingDevice
* Wrap SDL_Surface and positioning into Sprite class
* Move all rendering to rendering device
Rename Sprite::map_pos to Sprite::dest
Remove unused prio
Merge remote-tracking branch 'remotes/upstream/master' into rendering
Define Image class
Move remaining map rendering to context
FontEngine refactoring
Make screen private member of SDLRenderDevice
Do not segfault on faulty tile ids, but warn.
Merge pull request #914 from stefanbeller/tileids

Do not segfault on faulty tile ids, but warn.
Remove unused damage and absorb variables in StatBlock

Closes #913

Note, we'll probably want to update dmg_*_min values in flare-game to
1 if we want to keep the current behavior.
Merge pull request #915 from dorkster/fixes

Remove unused damage and absorb variables in StatBlock
Make Sprite::dest private
Wrap SDL_FillRect() into fillImageWithColor()
Try to fix clang build
Move all essential function prototypes to RenderDevice.h
Portuguese translation.
Wrap SDL_SetAlpha and SDL_SetColorKey
Turn Image #define into an Image class
Move more code to RenderDevice
Add setGamma and listModes to RenderDevice

setColorKey and setAlpha are now part of RenderDevice as well.