Disable nag notices

[deltafactory]

Suggestion: Wrap the require() calls in the main plugin file in the check for the DISABLE_NAG_NOTICES constant. This saves the file read time.

[deltafactory]

I think it also saves some DB/cache hits...

[jessuppi]

We might do this at some point, but for now the goal is to ensure timestamps in the database remain accurate regardless of nag notices being visible or not.