fix: API path for creating a DM channel via search

[nikkothari22]

Also fixed the following:

1. List of Raven Users on the sidebar with which DM is not created was running a get_list query. If the user does not have access to the "User" doctype, this would fail. Changed this call to get_all. This will be changed later since we only want to query Raven User - but names would not be matching due to "User" renames don't update "Raven User" #658.
2. When a Raven User is updated, we now update the User list as well as the channel list
3. User list fetched consists of both enabled and disabled users since there might be older messages for which we need to show names/avatars. But, while mentioning a user or adding them to a channel, we only enabled users. We would later also add a banner on DMs to inform users that a particular DM is disabled.
4. Website users can now be added as Raven Users
5. In Frappe v15, multiple role profiles can be attached to a user. This cannot be fetched via the list API since it's in a child table. Hence, when adding new users to Raven, if some users are not added, we show an error message in the dialog itself.