Added filters to manipulate the content of a production page.

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Removed obsolete template default for production event listings.
The same default template is already set inside the shortcode function.
@see WPT_Frontend::wpt_production_events()
Fake a session_start() to avoid PHP Warnings when Theater tries to start a new session.
Closes #67
Removed two commented lines of code.
Renamed the new filters to match the upcoming `WPT_Production_Page` class (see #68).
Removed a peace of commented code in `WPT_Production`.
Added a filter for the heading above event listings on product pages. Closes #69.

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Rewrote the `test_events_on_production_page_with_custom_heading()` test to support PHP 5.2.x.
Merge branch 'issue-67' into v0.9.5
Almost ready for 0.9.5!
Changed the order of the `wpt_production_page*` filters.
Merge branch 'production-page-content-filter' into v0.9.5
Temporarily unhook other Theater filters that hook into `the_content` to avoid loops.
Fixes #73.
Ready for v0.9.6.
The output of the {{remark}} placeholder was lacking wrappers divs.
Fixes #72.
Really ready for v0.9.6.