[FIX] REST tool handle DEV-44 in all cases

First "fix" for this issue (part of b2fa86a) did not work because .setValue() doesn't work when the CodeMirror element is hidden.

Second "fix" for this issue (060c5ad) didn't work in one particular case:
1. Choose a command that uses the POST method
2. Change method to GET
3. Change command to one that uses GET method
4. Change method to POST
---> POST body from previous command remains (despite being set to "", it didn't stick.)

This change (calling refresh on the cm_request object) should fix that.