simplifying error template rendering
fixing uploaded_file.py so that it no longer uses the browser's content type and content length

It is generally a bad idea to trust the client for this sort of thing, and this isn't just a theory - phantom was giving empty values for these fields, thus causing our tests to break
re-adding error logging on upload error

It was removed by mistake, so I'm re-adding it
changing UploadedFile to use mimetypes.guess_type() instead of magic.from_buffer

mimetypes.guess_type is better than magic at figuring out mimetypes
adding required steps to behave tests

The steps are required in order for the tests to pass
PEP8 changes
fixing bug - MAX_FILE_SIZE is exclusive

This fixes an off-by-one error
fix and re-include file upload tests

It is important that we test this functionality
removing unused import
skip features tagged use_splinter_client on Travis

Travis has problems running feature tests even though they run fine on our dev boxes, so we want to skip them for now
removing unused function

The function is no longer being used and we use another method to get the file size now that we have the filename
removing unused import

SEEK_END was mistakenly still being imported even though the function which used it was deleted in a previous commit
Merge github.com:alphagov/backdrop into fixing-file-upload

Conflicts:
	backdrop/write/admin_ui.py
Merge branch 'fixing-file-upload' of github.com:alphagov/backdrop into fixing-file-upload

Conflicts:
	backdrop/write/admin_ui.py
	backdrop/write/uploaded_file.py