[web] remove PropertySheet._cache
Instead of remembering that a css file has been processed, we re-process it at
every request. This prevents our cache getting out of date with the file
system. Closes #6893185
While we're at it, write the file atomically so that we don't risk serving
partial data.
\.svn
^build$
^dist$
\.egg-info$
^.tox$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
syntax: regexp
.*/data.*/database/.*\.sqlite
.*/data.*/database/.*\.config
.*/data/database/tmpdb.*
.*/data/ldapdb/.*
.*/data/uicache/
.*/data/cubes/.*/i18n/.*\.po
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/
data/pgdb/
data.*/pgdb.*