Rename #mw-mf-search to #searchInput

This is consistent with desktops naming convention for the
search box. I am rewriting the skin to be desktop friendly.

Note: haven't refactored mf-search.js to use overlay - that's
another exercise

Change-Id: I7867dcd4d9f7b477e19219fe6456713f15a3e714
Merge "Rename #mw-mf-search to #searchInput"