Convert awstats to an option of webstats
Integrated WEBSTATS_ADDON variable in imscp.conf
Updated CHANGELOG to reflect WEBSTATS_ADDON changes
At this stage piwik should not yet be a visible choice
Merge pull request #11 from i-MSCP/piwik_second_take

Convert awstats to an option of webstats, first step to make webstats Addon configurable