Create the tgcommon module

[optimumtact]

This is a VCS installed package that has common tg cogs functionality and the sqlalchemy schema files, so they can be referenced across multiple cogs.

[optimumtact]

pull in #6 as part of this module so that they're not required for each individual cog

[optimumtact]

This should probably be in a seperate repo, as some tooling doesn't support the subdirectory pip vcs setting