[ToDo] Dissect PR #60 into smaller, coherent PRs

[Olf0]

PR #60 by @Logic-gate intermingles some quite different topics, but each of them is definitely worth to be addressed. Though the convoluted character of PR #60 makes the various aspects of these topics very hard to review and discuss in an orderly manner.

Hence PR #60 should be dissected into single PRs, each covering one topic:

• WebDAV
• Thumbnails: migration from org.nemomobile.thumbnailer 1.0 to Nemo.Thumbnailer 1.0
• Starting apps: migration from xdg-open (utilities.openFile) to Qt.openUrlExternally
• Sharing: migration from Sailfish.TransferEngine 1.0 to Sailfish.Share 1.0; this is already split out to issue Adapt to SailfishOS' new (by v4.2.0) sharing API #83.
• port.text fix
• Other fixes

Beautifications (primarily proper code formatting) may be introduced along the individual, topic-related changes.

The code changes @Logic-gate did are looking good, the biggest concern is that these changes do not take backward compatibility into account. Some conditional compiling has to be introduced (see the SailfishOS:Chum GUI application as an example), as already discussed in PR #60 (see discussion there for further details).

P.S.: @Logic-gate created a detailed, tool-based planning, some aspects of which appear to be worth considering. In hindsight, this very detailed planning appears to be in stark contrast to the convoluted character of PR #60; my personal conclusion is that smaller, coherent PRs may allow for the complete planning to be mapped to the much simpler tools here at GitHub, as "Projects" and "Issues".

P.P.S.: @Logic-gate also published a testing release, which incorporates the current state of PR #60.