[Development] Closing issues automatically with new keyword

[Frederik Gladhorn]

Quick status update from my side:
I have the script running against a test installation of JIRA. It seems to 
work, there are some small issues to be worked out still.

- Qt Creator version numbers are verbose, so I need to be more generous in 
matching strings, right now I don't detect the version number correctly there. 
This one I will fix, it's just going to take a few minutes.

- Qt 3D Studio seems to be a mess, it has 5.x branches but the JIRA versions 
are 2.x, I consider this a won't fix.

I'd love if people started using "Fixes:", it will work retro-actively. And if 
you manually close a task in the meantime, no harm is done.

Multiple fix versions:
There were some doubts about which fix versions would be set, for example 
during the down-merge. This actually turns out to work quite nicely:
If a change ends up in dev, the script will detect that it will end up in 
5.13.0 right now and sets that as fix version. If the downmerge happens, the 
script will see the change again in 5.12.0 and add that fix version. In my 
opinion there is no major harm.
If the change is then cherry-picked to 5.9.7, it will also add that fix 
version.

This also means that changes going into 5.11.4 will be marked as fixed in 
5.12.1 or whatever is applicable branch/version wise. So we will actually set 
fix versions nicely.

There are some fixes in JIRA that would be easy to make, assuming there is 
agreement. Since I have to use some heuristics, I decided to only ever look at 
full version numbers, including patch level releases.
Currently we have version numbers in JIRA which do not make much sense to me, 
since they will never be released, such as 6.0, 5.12 and a few more. I would 
propose we always use the full version, so 6.0.0 and 5.12.0.
If the script finds 5.13 but not 5.13.0 it will not set any fix version.

I'm unsure where the whole thing should live, currently it's internal to The 
Qt Company, I'd love to publish it somewhere (it's a bunch of python files).

Cheers,
Frederik