T3460
Add support for op_return_raw input to Cashtab's SendXec UI.
Currently, this can be set by `bip21`. However, it is confusing and scary when it is set this way, because there is no parsing of the `op_return_raw` string -- so the user does not know what the tx is.
Add parsing and render a preview window of the parsed op_return_raw. Support all protocols known to Cashtab.
Instead of the kind of useless "bip 21 alert" divs -- we now just configure the form the way a user would do manually and disable the inputs.
The "webapp tx request" is preserved, for now. Will clean this up in a separate diff.