Improve import_from_uri to discover the mimetype of the file

[lvieirajr]

Currently import_from_uri only resolves which plugin it will use based on the file extension, something that can be easily changed to mask the real type of the file.

It would be a nice addition to rows if import_from_uri could recognize the mimetype of the file, instead of looking at the extension.

Some useful packages that could be used:

• filemagic
• python-magic

[turicas]

Related to #129.

[turicas]

Update on it (after some months...): I just uploaded the official version of file wrapper to the PyPI. We can install it by running:

pip install file-magic

And we can use to either detect the encoding or the file type, which could be used to solve this issue and also #129.

I've also written a blog post about file-magic library usage.

[turicas]

Note: the reasons to use file-magic instead of filemagic and python-magic are:

• We can install file-magic using both pip (pip install file-magic) and apt-get (apt-get install python-magic) so we won't have problems packaging rows to Debian (@kretcheu, look at this! Will change the dependencies on new version)
• It's the official implementation (maintained by file maintainers)