Lint HTML improvements

This changeset makes various improvements to the Lint error report:
the styles are now in a separate stylesheet, and the default style is
Holo-like. Paths are handled better when linting multiple projects
such that the report title includes the root-relative project path,
and all filenames are then relative to the project root. The table of
contents is now a table, and includes error and warning icons.

Change-Id: I4e49f7b226bfa4d7b46e3a29e006fe78a504e9ef
12 files changed