* wombat init fix:
- fix change from #339 which removed reiniting of wombat
- allow reiniting of wombat if inited via init_new_window_wombat()
- don't allow if reinited directly from <head>, as happened in document import
* tests: fix tests for 'new _WBWombat -> WombatInit' change
* wombat: window.frames optimization:
- since window.frames === window, no need for separate override!
- ensure init_new_window_wombat() is called on any returned window from object proxy
* support for 'classic' pywb features and misc improvements:
- add support for redirect to exact timestamp mode via 'redirect_to_exact: true' config setting
- tests: ensure memento headers added for redirect-to-exact
- memento: ensure Link header added for intermediate resources, check for 'enable_memento' before adding
- config: config passed to head_insert template as 'config'
- insert legacy 'vidrw.js' script if 'enable_flash_video_rewrite' config is set to true
- config: use_js_obj_proxy now defaults to true
- memento/tests: add proxy with custom accept-datetime test
