Update README with reference to Debian package

https://github.com/Nheko-Reborn/mtxclient/commit/023177170c4

Add new key for ubuntu repo that causes travis to fail.

Link mtxclient dynamically and update to Boost 1.69 for CI build

Simplify linkifyMessage.  Fixes #18.  Thanks @MonokelPinguin 

Parsing html as xml has inherent problems, most notable there are many
matrix clients that don't escape ampersands in urls of mx-replies, etc.
(See issue #18)

This also removes the replacement of <mx-reply> as it isn't strictly
needed.

Also the QRegExp is replaced with the Qt5 QRegularExpression for
perfomance and because it supports lookahead and lookbehind.

I'm pretty sure that the original code also replaced href="" with
href=\"\", which was probably wrong, but I'm not to sure about that.

Fixes #18

improve shell scripts and update .gitignore.  Thanks @zapashcanon 

Remove LICENSE file in favor of COPYING

Get rid of implicit conversion in text input height calculation.  Thanks @vtronko 

Don't let multiline text background overlap top border of text widget.  Fixes #39 
Thanks @vtronko