Improve library import speed

[roll]

From my tests it will take around 1s:

import jsontableschema

[pwalsh]

why?

[roll]

I don't know) I'll profile. There are a few chunks of code which runs outside of functions and classes. But also may be it's normal because of dependencies. Juts discovered it because GT time to create a report for simple dataset could be around 10-100ms but overall around 2s and most of them on jsontableschema import.

[Fak3]

The tabulator import is instant after the fix. But the jsontableschema is still slow to import... ;( I guess it was not only affected by tabulator, but has issue itself. Can you please have a look?

[roll]

FIXED
Latest tests just show not it's around normal (200ms). It still needs to read profiles from a disc.