sqldump does not store Controls properly

[raphaelahrens]

While working on #270 I realized when I run

python3 tm.py --sqldump test1.db
sqlite3 sqldump/test1.db 'SELECT * FROM Boundary;'

I get

Classification.UNKNOWN|TLSVersion.NONE|Internet||0|
2||<pytm.pytm.Controls object at 0x3acb78ae6cd0>||||True|2|Classification.UNKNOWN|TLSVersion.NONE|Server/DB||0|
3||<pytm.pytm.Controls object at 0x3acb78ae65d0>||||True|0|Classification.UNKNOWN|TLSVersion.NONE|AWS VPC||0|

The question is what should be a proper serialization of the Controls class?

In general is the sqldump feature a bit of a mystery to me, since the resulting database does not seem very usable. It just dumps the data into tables, but drops all relation information. This does not seem very useful.