Update gaia-ui-tests README install instructions

gaia-ui-tests used to be a separate project, but has since been merged
with the gaia project and is now outdated.  The instructions in the
README still mentioned the old project.
Update gaia-ui-tests README install instructions

Update gaia-ui-tests README install instructions to distinguish between
installing to simply run gaiatest and installing to develop gaiatest.
Update gaia-ui-tests README links and instructions

Corrected links in gaia-ui-tests README.md file and clarified some
instructions.

Conflicts:
	tests/python/gaia-ui-tests/README.md
Fix formating of gaia-ui-tests README
Fix formatting of gaia-tests-ui README
Fix formatting of gaia-ui-tests README
Fix documentation

Removed xfail from gaiatest options and removed explicit
acknowledge_risks='true' statement to force users to read and
understand the acknowledge risks page.
Removed Windows warning

Removed Windows warning because bug 832396 has been resolved