FEATURE COMPLETED: construct and upgrade buildings

Unbuilt buildings are displayed in the [build new modules] menu. The menu shows their info and allows for their construction.

Buildings' info on the colony management screen now displays all relevant info.

Added a new PHP function to load class-names. It auto-checks if the class is already loaded to avoid conflicts. Call with: load_class($name) where $name is the class name you want to load; just the name; not the file path; not the file extension.

Made some new mini-sized icons for resources to be displayed inline with text.

Made a nice looking "X" icon for closing sub-menus / screens.
see: media/themes/default/images/x.png