Several small fixes

[ksatyaki]

1. Frame ID from ros parameter - not hard-coded value.
2. @JonasHablitzelAVLD's tf2 fix
3. Add option to change which tf is being published (source and destination). This is now similar to what amcl would publish.
4. z-coordinate is always set to zero and altitude is ignored (for now). This can be reverted for the main repo, or a parameter can be added so that it is optionally published.