Respect system styling
Increase size of emojis (to remove empty space)
Add hover effect (partially adresses #41)
Less hardcoding of sizes
Use emoji font (color)

This reverts commit 4b807229.

When user is mentioned (via matrix 'highlight_count'), inactive
rooms will use a different color for the notification circle than
when only general unread messages exist.

work regardless of the theme choices the user makes.  The code
now incorporates the contrast between the background color and the
color generated by the user_name when picking colors.  It currently
has two 'big' issues:
1. Colors are not cached.  I am planning on adding a QHash for this
a little later.  This should improve performance by not calculating
the color for the same users over and over and over again.
2. Theme changes do not trigger the colors to get refreshed.
Currently, you will have to switch to a different room and back
to get the colors to refresh.

Update dark and system themes to provide
colors for the hover states for title, subtitle, and timestamp.

Add room list hover title/subtitle color change support.

fixes #331

fixes #235

fixes #204
fixes #255

fixes #40

fixes #245

fixes #264

* 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 

fixes #132