don't save empty records in asset editor

[kianzarrin]

Its redundant to add TM:PE data to an asset when there are no TM:PE rules. This redundancy has some downsides:

• If there is a bug in TMPE placing an asset would cause error even if asset creator created no TM:PE rules.
• this could potentially cause forward/backward compatibility issues
• performance (speed/memory)

All this inconvenience can be avoided by not recording Traffic rules if there is none.

Changes:

• Added bool ?Get/SetHasTrafficLights() which returns null/resets if traffic light value is not forced.
• added IsDefault() to IRecordables
• asset data is not saved (returns null) if all records have default traffic rules.
• null guards

TMPE.zip

[kianzarrin]

@krzychu124 good point. I saved traffic light move it record with old TMPE and loaded with new TMPE and it worked! both off and on state. its nice to know that binary serialization is cooperating for once!