Gravity Generators need to specify a subtype ID by default

Reported this previously as a bug and was told it's not a bug and to post it here. Quite simply put the Gravity Generator and Spherical Gravity Generator do not specify a subtype ID in the gravity SBC file. Quite simply put gravity generators need to specify a subtype ID in the SBC files. As is right now they are the only blocks that I have seen that do not specify a subtype ID. Currently as it sits now the gravity generators are the only types of blocks that I have seen that don't specify a subtype ID. This can potentially lead to crashing for any gravity generator type mod or similar item based around that type of block, especially if folks don't know how to go into the base files of the game to make a correction. Even the jump drive has a subtype ID specified by default in the SBC files as shown below.

<Id>
   <TypeId>JumpDrive</TypeId>
   <SubtypeId>LargeJumpDrive</SubtypeId>
</Id>

currently the gravity generator code sits as:

<Id>
  <TypeId>GravityGenerator</TypeId>
  <SubtypeId />
</Id>

A simple change of 2 lines of code could bring greater stability to gravity generator and gravity type mods as a whole.

<Id>
        <TypeId>GravityGenerator</TypeId>
        <SubtypeId>GravityGenerator</SubtypeId>
      </Id>

<Id>
        <TypeId>GravityGeneratorSphere</TypeId>
        <SubtypeId>GravityGeneratorSphere</SubtypeId>
      </Id>

Folks can make the changes above to the base files of the game, however it will get overridden with each update to the game or verification. Having blocks as a whole specify subtype IDs will make modding as a whole potentially easier and more stable, especially for those who may not have the necessary knowledge of how to implement the fixes above. A very small change overall to the default files for greater stability of mods and less chance of a crash overall.