ID and class names fixed for Special:PageMigration with mw-tpm-sp prefix

The ID and class names used at Special:PageMigration are altered by adding
the mw-tpm-sp prefix and BEM approach has been used. Grid layout has been
adapted and the necessary changes have been made in the methods to have
working features as per new layout. The edit feature is now removed and
target units are always editable.

Bug: 65736
Bug: 65898
Change-Id: Ieda6beebfa1303a15ae18513970c7bd7da84c755
Merge "ID and class names fixed for Special:PageMigration with mw-tpm-sp prefix"