Supplementary suggestions to !649

This implements all the suggestions and proposed design in !649 (closed). Overall I'm pretty satisfied with the result: it enhances symmetry and removes a few borders that looked a bit old fashioned in my opinion. Here are the last remaining imperfections, which I would be fine with having fixed in later MRs:

• on Chrome Mobile, titles may overflow the container box.
• on mobile in general, the buttons are stacked up, while they probably should be laid out inline.
• on Firefox for Android, the switch button has a white background, for some reason. [edit] worked around by adding a lightgrey border on mobile
• on Firefox for Android, the transaction title may overflow the container box.

@nicofrand, can you have a look please? And if you have any suggestions to fix any of the items above, that would be great. Thanks, and great work on the initial MR.

Closes #609 (closed).