Working regular expression filters

There's already [_some_ functionality](https://docs.ohsome.org/java/oshdb/0.5.10/aggregated/org/heigit/bigspatialdata/oshdb/api/mapreducer/MapReducer.html#osmTag(java.lang.String,java.util.regex.Pattern)) in the OSHDB to filter by OSM tags using regular expressions. But the current implementation does not work on distributed backends (Ignite) because of the non-serializable nature of connections to the _keytables_ database.

I see two possible ways to go forward:

1. implement a regex -> OSHDBTag matching on the client
2. if #225 is implemented (i.e. the string tables are distributed as well), regexes can be directly matched with the actualy OSM tags on the server