Read repo-info from /etc/cgitrc

Read repo-info from /etc/cgitrc

This makes cgit read all repo-info from the configfile, instead of scanning for
possible git-dirs below a common root path. This is primarily done to get
better security (separate physical path from logical repo-name).

In /etc/cgitrc each repo is registered with the following keys:

repo.url
repo.name
repo.path
repo.desc
repo.owner

Note:

*Required keys are repo.url and repo.path, all others are optional
*Each occurrence of repo.url starts a new repository registration
*Default value for repo.name is taken from repo.url
*The value of repo.url cannot contain characters with special meaning for
 urls (i.e. one of /?%&), while repo.name can contain anything.

Example:

repo.url=cgit-pub
repo.name=cgit/public
repo.path=/pub/git/cgit
repo.desc=My public cgit repo
repo.owner=Lars Hjemli

repo.url=cgit-priv
repo.name=cgit/private
repo.path=/home/larsh/src/cgit/.git
repo.desc=My private cgit repo
repo.owner=Lars Hjemli

Signed-off-by: Lars Hjemli <hjemli@gmail.com>