Use correct separator for "OR" condition in RSS rules

Although RSS rules were correctly parsed, the wrong separator for the
"OR" condition was used to re-generate the string of the rule displayed
in the preferences.

Closes #2205.
Don't use white spaces as separator in RSS "must not contain" rules

This RegExp uses both white spaces and | as separator.
Use only the latter and drop the RegExp as it is no longer required.
Merge pull request #2207 from pmzqla/rss-rules

Fix RSS "OR" condition in "must not contain" rules.
Right align header text that also has right-aligned row text. Closes #2188.
Don't display weird text in the 'Last Activity' column when the time is invalid.