Fix tagFilters implementation, adding tagFilters with OR relations

[quaaantumdev]

The current tagFilters implementation does not support OR relations, and it has implementation errors which should throw errors, but luckily dart/flutter does not throw (yet). This PR fixes both.

The bug fixed: _paramters['tagFilters'] is created as a List<List<String>> and is cast to a List<String>. Interestingly, this does not throw currently, but I guess there is no guarantee it will not throw one day.

The Feature added: Allow for a combination of AND and OR Tag filters such as: tag1 AND (tag2 OR tag3) AND (tag4 OR tag5) AND tag6 this is created by defining tagFilters like this:

{
  "tag1",
  [ "tag2", "tag3" ],
  [ "tag4", "tag5" ],
  "tag6"
}

would love to see this merged, thanks :)

happy if somebody wants to add some docs above but didn't take the time as most other functions do not have serious docs anyway

[quaaantumdev]

@nhathiwala would really like to see this merged :)