svn-support: Add subscriber to execute the svn.proxy.reload_cmd on config changes. #4271

svn-support: Add event to singnal apache mod dav svn configuration changes.

svn-support: Add reload command option (svn.proxy.reload_cmd) to ini files.

packaging: Fix versions of Chameleon(==2.24) and urllib3(==1.16).

subprocess: Change all imports from `subprocess` -> `subprocess32`

nix: Add subprocess32 to build inputs. From the python 2 docs: POSIX users (Linux, BSD, etc.) are strongly encouraged to install and use the much more recent subprocess32 module instead of the version included with python 2.7. It is a drop in replacement with better behavior in many situations.

svn-support: Add config setting to set the svn proxy (apache) reload command.

svn-support: Use settings functions from rhodecode config.

config: Add argument to convert settings to lowercase or not. Most settings should be converted to lowercase during app init. But at least file system paths should not lower cased. Threfore we need a switch to control it.

vcs: make the not initialiazed exception more meaningfull.