Clarify exclude vs patterns setting in Exclude UI

[m3nu]

Thank you for the flexible interface for "exclude"!

There is one point that is quite confusing in borg - and since Vorta is referring to the borg documentation, this applies to Vorta too.

In borg there are two distinct sets of options which can be used for excludes:
--exclude and --exclude-from
AND
--pattern or --patterns-from

Only the second set of options uses the term "pattern" in its name.
To cite the borg documentation:

A more general and easier to use way to define filename matching patterns exists with the --pattern and --patterns-from options. Using these, one may specify the backup roots, default pattern styles and patterns for inclusion and exclusion.

If I understand correctly, currently, Vorta only supports --exclude. This should be stressed in the user interface (which links to the borg documentation) to reduce the confusion.

Originally posted by @goebbe in #907 (comment)

[goebbe]

The following screenshot shows the "exclude dialog" in Vorta 0.9.1.

Perhaps, the following would be less confusing:

Title: Exclude files and folders
Dialog text:
Exclude files and folders from the backup. Exclude uses file name pattern matching (fnmatch) by default, see documentation. To add multiple patterns at once, use the "Raw" tab