General cleanup and internationalization (i18n) fixes.

CSS and JS are loaded separately in SkinCustard::setupSkinUserCss() to prevent a Flash of Unstyled Content.

Removed unused globals and swapped the used globals to their context-sensitive equivalents.

Made generateTab() i18n-compatible.

Fixed some str_replace() URL generation, hard-coded English strings and hard-coded URLs and whatnot.

The wfSuppressWarnings()/wfRestoreWarnings() should be removed and we should find out *if* there's anything causing E_NOTICEs and if so, fix 'em.

The sidebar parsing code should probably use my NestedMenuParser (https://gerrit.wikimedia.org/r/#/c/108045/) if and when that makes it into core.