This applies the new design for multiple buttons in the message action bar,
paving the way for more things to appear here.
In addition, this changes the existing options button to use the three vertical
dots icon. Some theme colors are also tweaked to align with what they were meant
to be from the unified palette.
Little bit of a mix of things in this one:
* Support variable-width dialogs. Default is fixed-width as before,
only UploadConformDialog is variable-width. Controlled by a prop
to BaseDialog.
* Fixes to the cancel 'x' - scale the mask image, tweak size & colour
* Colour & boldness of dialog titles
* Align the dialog title & cancel 'x'
* Remove gap between dialog buttons & right hand side of dialog(!)
* Round corners on dialogs
* Add grey border on image preview in upload confirm dialog
* and, squeezing in slightly randomly, finish the partially renamed
ChatInviteDialog to AddressPickerDialog.
* renames RoomTooltip to be a generic Tooltip (which it is)
* hooks it into Field to show validation results
* adds onValidate to Field to let Field instances call an arbitrary validation function
Rebased from @ara4n's https://github.com/matrix-org/matrix-react-sdk/pull/2550
by @jryans. Subsequent commits revise and adapt this work.
If the dark theme is activated, the country dropdown defaults to those colors
where it doesn't fit in with the always-light auth flow. This restyles its
colors to be light.
