Big part of PhysFS support

* removed -mod argument
* removed -datadir argument
* removed -lang argument
* removed some dead ui code
* added resource manager and file loaders (stream and SDL)
* changed interface textures location to match new directory structure
* removed CGameData for mod support
* added PhysFS support
Implemented libsndfile loader in PhysFS
More work on PhysFS support

* added output stream
* fixed music loading
Added Exist() to resource manager, updated model
More work on levels
More work on streams
Last changes
Fixed level list
Fixed music loading
Fixed texture and script loading
Fixed mission description loading
Merge branch 'dev' into dev-physfs

Conflicts:
	data
	src/app/gamedata.cpp
	src/ui/control.cpp
	src/ui/edit.cpp
	src/ui/maindialog.cpp
Help file loading
Fixed SatCom image loading

Now LoadTexture/SetTexture functions require full path with "textures/" directory
Added -mod commandline argument to add additional locations to physfs
Saving colobot.ini through physfs
Restored -datadir and -langdir arguments, added -savedir

Also, fixed some crashes when unable to open file
Add po4a to the command installing dependencies

There is an one-line command in the INSTALL.md for Ubuntu/Debian users which
installs all dependencies. po4a was listed above it, but it wasn't in the command itself.
Add missing dependency "gettext" for Ubuntu
Conflicts:
	INSTALL.md
Loading all mods found in "mods" directory