Preload access rights from file

[flesueur]

configparser is quite slow and can slow down from_file access rights on large collections.

For instance on my lab with 100,000 accounts, a PROPFIND on / lasts (with #2002 already integrated):

• 22 seconds with from_files
• 13 seconds with owner_only

The proposed patch extracts configparser settings during __init__() and stores them in a dict. In the same lab, the PROPFIND requests last 15 seconds, which is nearly as good as owner_only.

Note : I also tried to pre-compile regexps but this did not yield a visible performance improvement, configparser really seems to be the bottleneck here.

[flesueur]

Working on mypy...

[pbiering]

Makes sense