mender-convert: UI

In MEN-1812, we create CLI tools to convert images to support Mender.
In order to improve ease of use, in particular for prototyping and demo cases, it would be nice to have a UI on top of this CLI.
This UI will run locally (e.g. on a laptop) because the disk image files can be very large and it is much faster to process them locally.

User value (why)

• Easier to get started with mender-convert, no need to learn about CLI options

Size (SP)

• TBD

Acceptance criteria

• It is possible to use a SD card or (possible compressed) .img file as input
• It is possible to configure server (URL, user, pass) once and re-use this configuration across future conversions
• Credentials are stored securely (e.g. just store token in home dir and ask for password if token expires, like mender-cli)
• The UI is cross platform and can easily run on Linux, Mac and Windows (e.g. python / web framework that can be packaged portably)
• (stretch goal) It is possible to upload Artifact to the configured Mender server after successful generation