Big graphical update

This patch contains a number of features/fixes that make the game feel move alive and responsive, I've just got a couple more things to smooth out around the actual in-game interactions and effects, then I'm going to start looking to flesh out the rest of the tech tree and balancing.

Patch notes:

• Finished aligning a lot of the tiles to work more with the 2d style.
• Added a shader to render grass blades on the grassland tiles
• Added a shader to to ocean tile to provide some movement/transparency
• Updated logic when opening the context menu to automatically detect screen size and render the action tiles appropriately sized
• Added a loader dialog when starting/loading a single player game so it doesn't look like the game has frozen for a second.
• Fixed a bug that meant AI would stop taking their turn when loading back into a game.
• Corrected logic that was preventing the weather system from rendering different states.
• Added a 'Movement Speed' slider to the settings to control the speed that units move around the map