Rename the repository to inbuxa-webmail

The repository moved from inbuxa/ihasmail-inbuxa to inbuxa/inbuxa-webmail,
matching inbuxa-server and inbuxa-admin. Point the source links, the image
name and the package link at the new name. The OAuth client id stays
ihasmail-inbuxa, since that is what the server registers.

.env.example

@@ -75,7 +75,7 @@ APP_NAME=ihasmail
 # you have patched it, point this at your own tree. Shown on the sign-in page
 # and in Settings > About. INBUXA's webmail is itself a modified ihasmail, so
 # the default is this fork.
-SOURCE_URL=https://git.coffeylabs.org/inbuxa/ihasmail-inbuxa
+SOURCE_URL=https://git.coffeylabs.org/inbuxa/inbuxa-webmail
 
 # ---- Settings this installation decides (all optional) ----
 #