Refactor copy-pasted securityLevel filters

[todofixthis]

There's a lot of copy-pasted code for validating securityLevel in certain command filters:

'securityLevel': f.Type(int) | f.Min(1) | f.Max(3) | f.Optional(default=AddressGenerator.DEFAULT_SECURITY_LEVEL),

We could convert this into a filter macro in iota/filters.py to ensure consistency. As a bonus, we could also remove a bunch of duplicate unit tests.

[todofixthis]

Scheduled for release: 2.0.6