docs: Fix a few typos

[timgates42]

There are small typos in:

• CONTRIBUTING.md
• symposion/reviews/utils.py
• symposion/sponsorship/models.py
• symposion/static/tabletools/js/TableTools.js

Fixes:

• Should read there rather than ther.
• Should read separate rather than seperate.
• Should read namespace rather than namesapce.
• Should read incomplete rather than incomplate.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md