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.
Follow project coding style. Issue #2192.
Stop using internal libtorrent API. Closes #2202.
Use parse_magnet_uri() where possible.
Remove useless includes.
Revert "Temporarily disable Travis CI tests against libtorrent 1.0.x until #1878 is resolved."

This reverts commit 7029f4dcd2f123014b93718ee8da68ce8e1558e7.
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.
Update coding style. Closes #2091.
Add hotkeys and buttons for Top and Bottom priorities