fixes #437

When the object is destroyed the connections will be removed
automatically by Qt.

fixes #433

[ci skip]

fixes #235

NHEKO_ALLOW_INSECURE_CONNECTIONS=1 ./nheko

fixes #260

fixes #264

fixes #233
fixes #89

* Refactor widget items to use same interface

* Support audio, video, generic file for pasting

* Add utils function for human readable file sizes

* Set correct MIME type for media messages

This change also determines the size of the upload once from the
ContentLengthHeader, rather than seeking the QIODevice and asking for
its size. This prevents any future trouble in case the QIODevice is
sequential (cannot be seeked). The MIME type is also determined at
upload once, rather than using the QIODevice and the underlying data
inside.

* Allow for file urls to be used as fall-back

This fixes an issue on macOS which uses `text/uri-list` for copying
files to the clipboard.

fixes #228 

Show a better message on the login screen after an initial sync failure.

fixes #86
fixes #89

When a custom filter is inserted into nheko.conf or there was no filter
defined yet the default filter gets automatically uploaded.
After a successful upload the server-side generated filter-id is used.

This is done async as it is just an enhancement and it is not required
to upload the filter before the first request.

[ci skip]

I had a look at sync.cpp and checked which parts of the sync response
are currently handled and which not. As I think it is unnecessary to let the 
unhandled data be transmitted without being handled I added these filters.

In the same term I increased the timeout server-side to 30s as Riot
defaults to this value as well. Especially now when a lots of presence-updates 
are not send anymore this value is more relevant.

It is now also possible to use a filter that is defined in`client/sync_filter`.
Advanced users might want to set an own filter here.

[ci skip]

fixes #132 

fixes #107

fixes #25