The track license lock key should be hashed under lmdb and spared from removal

Unfortunately the track_license key can be very long and cannot then be stored under lmdb.

The track_license key needs two things :
1. be MD5 hashed before it is stored under lmdb
2. be flagged as not removable by replacing first character of its MD5 hash by 'X'

This pull request should fix a segfault in cf-hub