Adding MetricsFormatter class which knows how to format/display metrics (time, money, size, etc)

Fixes #4063, allow csv renderer to handle arbitrarily nested data structures at least a little bit gracefully.

Refs #4087, rewrote UI integration tests to use phantomjs or slimerjs and added (disabled) UI tests to travis build config.

Notes:
  * Modified main page-loading JavaScript to use ajaxHelper so it's possible to know when all AJAX requests are made.
  * Add setUrl method to ajaxHelper so it can be used when a doing AJAX w/ a URL instead of an object containing query parameters.

Refs #4041, #4040 add new CoreVisualizations plugin and move HtmlTable, Cloud & JqplotGraph visualizations to it and improve UIIntegration test debug output.

Added namespaces to functions.php files in the five plugins that had one
Work in progress

renaming Unzip to Uncompress,
Renaming Tracker/Referer to Tracker/Referrer,
and few more

Removed many Piwik_ functions, in Piwik 2 it is best practise to use the methods calls instead

Todo: finish converting core/ classes + convert plugins/ classes to use \Piwik\Plugin namespace + fix build + Merge master

Refs #4059 Work in progress: Conversion to use Namespaces: Period*, Metrics, Segment, SegmentExpression, PluginsManager.
Removed some deprecated code.

Converting Access & Auth to namespace

Notice that auto refactoring has created a nested namespace. Not sure this is what we want - so we might have to edit those nested namespaces afterwards (I think they don't look so good)

Notice that auto refactoring has created a nested namespace. Not sure this is what we want - so we might have to edit those nested namespaces afterwards (I think they don't look so good)

2 steps required:

1. Refactor > Move > \Piwik\Core\Config (uncheck "Create new File")
2. Refactor > Rename > Piwik_Config to Config

Notes:
  - Modified ManySitesImportedLogs fixture to add segments if desired.
  - Switch to synchronous execution of curl requests until deadlocking issue in archive processing is dealt with.
  - Fixed bug in LogAggregator where if a segment required a subquery, archiving would failed.