Rer.solrpush

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- Fix tika indexing parameters: now modified and created dates are correctly indexed.
[cekk]

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- Refactor elevate control panel and use collective.z3cform.jsonwidget.
[cekk]
- Some improvements in indexing.
[cekk]

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- Fix logic in maintenance view.
[cekk]

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- Fix maintenance sync view.
[cekk]

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- Fix encoding problems in `escape_special_characters` method for python2.
[cekk]
- Remove collective.z3cform.datagrifield dependency and temporary disable elevate control panel.
[cekk]

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- Fix date indexes in query when they already are in "solr syntax".
[cekk]