Update 0.30

Another mostly technical update: lava spells for sandbox and technical stuff for future mod support.

• Added lava source, sink and globe spells for use in the sandbox mode.

• Switched to physfs library for reading/writing game files. Building editor now saves to %APPDATA%\buildings\ folder.

• Optimized file checks (like reloading shaders/textures/scripts).

• Switched to Visual C++ 2013. No runtime installation necessary, so ignore this.

• Changed button style in the main menu.