Backport upstream fixes for regression in Akonadi and PIM (stack rebuild)

Upstream KDE have recommended backporting the two following commits to 18.12.3

Request/advisory from KDE: https://mail.kde.org/pipermail/distributions/2019-April/000314.html

**** email ****

"recently a bad regression was spotted in Akonadi, which causes all mails to be
repeatedly downloaded and if you have a lot of mails, this can overload
everything and cause further issues down the road.

The fix will be in 19.04 RC onwards, but also the 18.12 branch is affected.
Since there will be no more 18.12 releases, if you need to keep that version
in your repositories you may want to apply the following patches:

- https://commits.kde.org/akonadi/1d8851495bcfa6ff5d3fa35882b68fdf68b21a7f
- https://commits.kde.org/akonadi/53ad3b6d73d92ea289cf0183c10e2b8a35c8127a

Note that since the change touches an inlined method, you will need to rebuild
all PIM (or at least, everything that uses that code)."

**** end email ****

From IRC:

[10:28] <einar77_work> it fixes quite a bad regression (note, it is inlined code, so everything using it must be rebuilt)
[10:33] <einar77_work> acheronuk: major regression, will force mail to be redownloaded all the time every mail check
[10:33] <einar77_work> this in turn may hog the akonadi server, leading to deadlocks and other issues

Backport is from 19.04 branch, and fix is referenced in: https://mail.kde.org/pipermail/release-team/2019-April/011299.html

"* Akonadi got a very important fix in an inlined method. It is required to recompile the complete KDEPIM stack."