(bug 52387) Special page for querying by property value.

REQUIRES I69c0b50 in Wikibase repository. 

Special:SimpleQuery allows to query for a value used in a property-value Snak.
Queries will still not work via the special page since the backend
is not yet fit to handle the queries.

Currently, the value field requires input of the data value as JSON, e.g.:
{
  "type":"time",
  "value":{
    "time":"+00000000002-01-21T00:00:00Z",
    "timezone":0,
    "before":0,
    "after":0,
    "precision":11,
    "calendarmodel":"http://www.wikidata.org/entity/Q1985786"
  },
}

This is currently necessary because there is no parser for Time values in the backend.
In the future there could also be a field for the "type" and one for the "value", for now
allowing to copy/paste into one single field might be more convenient.

In a follow up, the JavaScript UI should be used to allow entering values in a more convenient
way.

Change-Id: If089492726d2745158c646e3ca568d14754fb692
Remove SimpleQuery::CACHE_TTL_IN_SECONDS

REQUIRES Id99fb2407 to be merged in Wikibase repository

Change-Id: If416ccc384151cf0a8b03b7ebf074e65299ebcbe
Merge changes If416ccc3,If0894927

* changes:
  Remove SimpleQuery::CACHE_TTL_IN_SECONDS
  (bug 52387) Special page for querying by property value.