Activate Travis build and fix scripts to comply with flake8 standards

This PR adds a .travis.yml file at the top-level of the repository running `flake8` on all the Python scripts. It also fixes individual scripts to comply with flake8 standards and let the Travis build pass.

- [x] omero/analysis_scripts/Kymograph.py
- [x] omero/analysis_scripts/Kymograph_Analysis.py
- [x] omero/analysis_scripts/Plot_Profile.py
- [x] omero/export_scripts/Batch_Image_Export.py
- [x] omero/export_scripts/Make_Movie.py
- [x] omero/figure_scripts/Movie_Figure.py
- [x] omero/figure_scripts/Movie_ROI_Figure.py
- [x] omero/figure_scripts/ROI_Split_Figure.py
- [x] omero/figure_scripts/Split_View_Figure.py
- [x] omero/figure_scripts/Thumbnail_Figure.py
- [x] omero/import_scripts/Populate_ROI.py
- [x] omero/setup_scripts/FLIM_initialise.py
- [x] omero/util_scripts/Channel_Offsets.py
- [x] omero/util_scripts/Combine_Images.py
- [x] omero/util_scripts/Dataset_To_Plate.py
- [x] omero/util_scripts/Images_From_ROIs.py

To test this PR:
- check the changes do not break any script functionality in the deployed server
- check https://travis-ci.org/sbesson/scripts is green