some service scan improovements

some service scan improovements
- add a only free scan
- the scan now finds also services not listed in SDT
- add option "clear before scan" also for single transponder searches

For the only free scan a change in the main lamedb transponder format was
needed... i think this breaks some external settings editors

To detect the service format now the service database file starts with "eDVB
services /4/" .. the old format was "eDVB services /3/" .. e2 can read the
old and the new format.. but it writes always the new format!