fix #3527: bad query string

Let's hope that the bad formatting occurring for, at least, very small
negative values in `String.format()` with a `null` Locale will not
happen with `StringBuilder.append(double)`.
Merge branch 'release' into upstream
Use RxJava for status updates rather than own observers
Use RxJava for direction and geodata updates rather than own observers
Remove now unused classes
Emit parallel queries to connectors when searching
Not to merge: check imbrication status of geodata provider
Obtain address with rxJava
There can be no null coordinates and no exception