Add 'wpsf_restrict_manage_social_metrics' action

Added 'wpsf_restrict_manage_social_metrics' action to
SocialMetricsTable which allows me to add custom filters to the social
metrics results.
Cleaned up the dashboard sorting queries

Cleaned up the dashboard sorting queries and moved them to a
‘pre_get_posts’ filter.
Add 'smt_dashboard_query' filter.

Had to add a way to filter the dashboard query because it wasn’t
picking up my custom query vars.
Changed name of 'restrict_manage_social_metrics'

Changed the name of the 'wpsf_restrict_manage_social_metrics' action to
'wpsf_restrict_manage_social_metrics_dashboard’.
Changed name of 'restrict_manage_social_metrics'

Changed the name of the 'wpsf_restrict_manage_social_metrics_dashboard'
action to
‘smt_restrict_manage_social_metrics_dashboard’. This makes more sense.
Fixed weird code thing

It was just some weird alignment issue that bugged me.
Adding comments

Comments are good for the soul.
Code cleanup

Moved smt_handle_dasbhoard_sorting() into the SocialMetricsTable class;
renamed action hook ‘smt_restrict_manage_social_metrics_dashboard’ to
more closely match the filter it is associated with;
Merge branch 'pr/16' into development