Convert datetime to str when creating a DTA

Closes #71
Merge pull request #72 from guewen/8.0-create-dta-date-error

Convert datetime to str when creating a DTA
Separated Lint tests
Remove deprecated travis_run_flake8
Remove .travis file we already have .travis.yml
Merge pull request #73 from yvaucher/8.0-separate-lint

Separated Lint tests
Move payment slip
Port bank to new api
Port company to new API
Extracting payment slip related knowledge

into a new model dedicated to payment slip
Moving media into static
Changing company defaults for payment_slip
Moving font file into static
Adding QWeb report skeletton
Payment slip is know draw using PIL
Fix New API syntax error when proting and remove dead files
Fix invalid variable name
Import payment slip model
Add first version of new payment slip report
Adjusting Slip element position