Misc fixes

[dartcafe]

• Fixed display of creation time

• Added a few public endpoints for share management

• Maintenance and refactorings:

  • Renamed constant Poll::PERMISSION_POLL_VIEW to Poll::PERMISSION_POLL_ACCESS
  • Removed obsolete tidy step
  • Fixed some typecasts
  • Pack PollManager and removed duplicated code

• Updated schema definition

  • Fixed db types and defaults to match unique share index
  • Removed FK constraint for share table
  • Added unique index for share tokens

• Reworked poll access via shares

Hopefully addressing #4206 and related issues

With 20cd64f some fundamental changes have been introduced. Goal is to support more performant queries

• Added some indices to help complex joins and optimized the index
  Eventually there are some more to add.
• Introduced new binary hashed columns over pollOptionText and pollId for unique index and join selections
  • polls_votes -> vote_option_hash_bin
  • polls_options -> poll_option_hash_bin
    Seems that the binary hash is not usable with PostgreSQL this way. Rolled back to the string hash but keep the functionality
• decrease column width of vote_option_hash and poll_option_hash from 256 to 32 bytes
• removed creation of optional indices from all migration and repair steps and support AddMissingIndicesEvent
  The optional indices can then be created with occ db:add-missing-indices.
  New installations will still create the optional indices on install time
• Separated the commands in more granular index and database commands; updated the hints for the console output
• Adjust icon style

before	after

• Added Nextcloud version compatibility batch to readme
• Moved information from readme to the wiki
  • Added occ documentation to the wiki
  • Added some installation information and help to the wiki