Fixed: the second step of the entry tour was misplaced if the entry was changed state (e.g. from read to unread) while in the third step, and the user went back in the tour.

To fix this, the "mark read" and "mark unread" entry buttons have been wrapped in a button-group div, which is always visible for open entries. The second step of the tour is passed this div as its target, so that positioning is correct.
Removed unnecessary CSS filters in the feed tour targets.

The targeted elements should be always visible when the feed tour starts, it should not be necessary to filter them by visibility. Also this makes the selector simpler, which will help readability and maintenability.
Removed "Back" button from all tours.

It was too much trouble. Because of the dynamic nature of the app pages, elements could move or disappear which could cause tour bubbles to be misplaced or missing when going back. It's simpler to just remove the Back button. Tours can be reset from the profile page if the user wants to go through them again, anyway.
Mobile tour step now points to a button-group wrapping the show/hide sidebar buttons.

This way the tour points to an always-visible element, which fixes positioning problems.
Mobile tour step is now targeted to a navbar element, with an offset.

This ensures that the targeted element is always visible, which fixes some positioning problems. The offset is intended to make the bubble arrow point at the swipeable area, instead of pointing to the navbar (which cannot be swiped).
Simplified target of a step in the main app tour. This required reworking the show/hide read entries button in the navbar.

This shouldn't be perceptible for the user, but now the tour step targets an element that is always visible (the <li> that wraps both buttons, only one of which is visible at any given time). This fixes some potential placement issues with the tour bubble placement.

An aditional option (container: "body") has been added via data- attributes for the boostrap tooltips of both buttons. This is necessary because otherwise bootstrap uses a too small width for tooltips, which would look ugly.