SOLIDPOD: add clear button next to select webId in permission form

[jesscmoore]

Describe the Bug

The webId selection needs clearing, if a user wants to change the webid entered in the form.

add a 'Clear' button next to the 'Select webId/s' button in the individual/group webid input section, as this section of the form needs clearing correctly when a user enters a webid, then switches to another recipient type and returns, and wants to enter a different webid.

As first raised in PR comment #560 (comment)

Expected Behaviour

A user should be able to deselect a webid selected in the grant permisison form

Screenshots

[If applicable, add screenshots to help explain your problem.]

Context

Where has the issue been observed:

• Android
• Chrome
• iOS
• Linux
• macOS
• Web
• Windows

Closing Criteria

Checklist for closing the issue:

• No errors from make prep
• All tests pass make qtest
• [Issue specific requirements.]