Option to make profiling disabled by default

Add a configuration option to start profiler disabled. Check it value
to decide if profiling should be skipped for each page. Profiling can be
re-enabled by setting the query parameter pp=enable.
Changed configuration option to enable/disable profiling

Set Cofiguration.enabled to false to disable functionality, set it to true to
re-enable. Default value is true.
Merge pull request #23 from gkats/master

Option to make profiling disabled by default