Gphotos-sync

Minor features and bug fixes:-

- update dependencies for security patches
- add an option for flat folder structure YYYY-MM (thanks idoroseman)
- add an option to rename the photos and albums folders (thanks idoroseman)
- fix date range bug on --rescan
- fix extraction of EXIF description into DB on comparison
- fixes to make the comparison feature more accurate with duplicate file names
- add --favourites-only flag
- add Python3.6 to the Travis test matrix
- add readme for Python3.6

Add the --album option to sync a sinle album.

Update to Python 3.7 and reduce dependency issues (in particular magic library)
Minor fixes to the comparison feature to reduce false duplicates.
New GPS Location extraction feature (Beta) - will scrape Google Photos Website for the missing location information that the API omits - currently only adds this to the SQL index, but will, in future, update the JPGs with this information.

Now indexes and downloads files in shared albums (but only if the album has a title).
Option to change the log logfile name and location
Better test coverage

Now album links are unique names, avoids name clashes in album folders.
Also, albums folders can move to a new path if their dates change.