PLUS : Coal Power Plants

* Coal Power Plants are now the default power plant available from level
1
* Coal Power Plants cost between Wind Turbines and Nuclear Power Plants
* the resource gain is between both
* the pollution is bigger
* Cost for nuclear power plants raised, pollution lowered
* Resource Gain for Wind Turbines lowered
BUG FIX : GUI text location based on resolution

* The GUI text wouldn't be visibile on certain resolutions, so I made
the display location be based on the actual screen width and height.
PLUS : Solar Panels

* Solar panels don't pollute
* Solar panels give as many resources as wind turbines
* Solar panels cost 600 resources
* Fixed the ability to purchase Nuclear power plants even though you
didn't have 800 resources,getting a negative resource amount.
PLUS : Saving level progress

* After each level we set the "Levels Unlocked" to the level we passed +
1, being able to later access for example if we passed level 2, levels
from 1 to 3.
* Started to work on the main menu of the game
* Made a GuiSkin which has values changed for labels
* Imported a font.
PLUS : Main menu depending on available levels

* main menu will be displayed based on the number of levels that have
been finished.
PLUS : Levels can now be accessed from the menu

* Still have an issue with coroutines, it only works if I start it once.