Use wgResourceBasePath instead of wgScriptPath for wgStylePath etc.

Use wgResourceBasePath instead of wgScriptPath for wgStylePath etc.

This make re-configuring these much easier by only needing to update
one variable instead of four.

Also remove redundant hardcoding of wgStylePath and wgResourceBasePath
in the generated LocalSettings.php file during installation. This way
changing wgScriptPath will naturally result in the other variables
updating too. We already do this for many other variables (such as
wgLoadScript, wgScript, wgExtensionAssetsPath, etc.).

Change-Id: Ide74355b4054c78214c17f3b2d6fa2f5270e0ab9