Allow read only permissions for viewing databases

[EthanS94]

There will likely be usecases where one user wants to share a database with another user without letting that other user delete/edit the database. It is not uncommon to open up files with read only permissions. Currently, pycinema doesn't support this do to the use of r+ in the various reader filters which causes a permission error for read only files. Can the r+ in all reader filters be changed to a r?

Thanks

[dhrogers]

This makes sense to me, especially with the segmentation of operations into filters. I'll do a pass through the code and see if there are any issues with this.