base/uuid: Prevent initialization races

Using statics inside functions C++ guarantees initialization (thread safe even)
orly/core_import: Initializing variables always is a good habit
Use Twister UUID generation rather than Best for Twitter dataset

The global static initialization order bug is gone now for TUuid
base/uuid: Use constexprs for StrSize / MinBufSize

Makes them compile away more, and be thread safe.
Merge pull request #104 from cmaloney/misc_import_fixes

Misc import fixes