[opt-viewer] Add --filter option to select remarks for displaying.

This allows limiting the displayed remarks to the ones with names
matching the filter (regular) expression.

Generating html pages for a larger project with optimization remarks can
result in a huge HTML documents and using --filter allows to focus on a
set of interesting remarks.

Reviewers: hfinkel, anemet, thegameg, serge-sans-paille

Reviewed By: anemet

Differential Revision: https://reviews.llvm.org/D57827

llvm-svn: 353322