html: put 'use strict' on separate lines

use.py:
import re
import sys
for fn in sys.argv[1:]:
with open(fn) as f:
s = f.read()
s = re.sub(r'''(<script>)('use strict';)\n( *)''', r'''\1\n\3\2\n\3''', s)
with open(fn, 'w') as f:
f.write(s)

python use.py $(hg loc 'kallithea/templates/**.html')

js: use strict ... and fix the problems it points out

"use strict" gives stricter checks, both statically and at runtime. The
strictness tightens up the code and prevents some kinds of problems.

The <script> tag addition might not be pretty, but has consistently been added
with:

sed -i 's,<script>$,&'"'"'use strict'"'"';,g' `hg loc '*.html'`

lib: handle both HTML, unsafe strings, and exceptions passed to helpers.flash()

Before, h.flash would trust any input to contain html ... and callers would
convert exceptions to string, often with a simple str() or unicode() ... which
really didn't deserve to be trusted.

Instead, only trust messages that have a __html__ and escape anything else ...
but also apply str/unicode on the parameter so the caller doesn't have to but
*can* pass an exception directly.

helpers: refactor flash - drop unnecessary subclassing, and just wrap using helper functions

Mainly dedenting.

styling: map pylonslib flash message categories to bootstrap alert classes

Error messages where shown without styling because they use the alert-error
class which doesn't exist in Bootstrap.

Pylonslib only support a few hardcoded categories. Map them to corresponding
Bootstrap classes.

Second step in two-part process to rename directories.
This is the actual directory rename.