CompatibleProfile: return null or dummy profile for missing profiles? also: standardize clearing behavior

[crashdemons]

ref #52

new issue to indicate the lower priority nature of this

[crashdemons]

to ease this though, there are new methods in 5.2.14:
CompatibleProfile:hasRequiredFields() which checks if id and/or name are set.
CompatibleProfile.isValid( profile ) which combines that check with a null check

using these in the future may simplify a lot of code. although return null for a lack of profile is still preferable to a null profile.
The dummy profile serves almost the same purpose as a null profile though in that both are for the same case (no profile present)

However, consider:

• setting an empty or null profile to "clear" existing profile from a skull may be unwanted
• having a standard way to clear a profile from a skull may be wanted though
• currently, setting a null compatibleprofile will cause an NPE (it tries to get the internal object first)
• currently, setting a dummy profile will cause an IAE (creating a GameProfile with null id, null name)

It will be important to define and standardize which ways can and can't be used for setting/clearing going forward.

[crashdemons]

5.2.14-SNAPSHOT will standardize a clearing method, but the question remains