As a Studio user, I can upload a custom icon

An import button is available in Studio Designer buttons and drawer menu entries screens

AC

• When uploading an icon, format is restricted to svg
• Svg file is validated to avoid corrupting the iconset
• I can see an indication that icon is being uploaded (bonus)
• Icon is named based on the file name without its extension (i.e. no .svg)
• If icon name already exists, icon is renamed into something that is not conflicting (e.g. toto_1, toto_2)
• When icon is uploaded, it is automatically selected
• Uploading an icon replaces any existing selection made
• Uploaded icons are stored in a single custom iconset for the whole project
• If the custom iconset does not exist, it is created
• If icon is the wrong format, an error message is displayed and the icon is not uploaded:

Icon was not uploaded: file format has to be svg