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.
Also fairly significant refactor of the uploading code: there are
a number of different ways of triggerring a file upload and each
went through a different code path (the media config size limit
worked on one of those paths). Basically take a lot of code out
of the views and put it into ContentMessages.
Sorry about the size of this patch.
https://github.com/vector-im/riot-web/issues/7565
