Invalid alias format message is useless

[ssbarnea]

When someone is trying to add a room alias, they will get a "Invalid alias format", one message that does not include any cloue regarding what would count as a valid alias format, neither a link to a web page that would document the "format".

[lampholder]

Slightly related to #7372 (in which I gripe about the term alias being used at all).

This UX:

should be modified such that you:

• don't need to type in the non-optional components of a room alias (the leading # and the trailing :domain.tld)
• get feedback when you try and type an illegal character (perhaps something like http://jsfiddle.net/5ocu2cqk/20/ , though I know people have strong feelings about UX that just refuses to accept your invalid keypresses [as opposed to acceptiong them and then highlighting that they are invalid])

[lampholder]

p1 'cause if we're tackling #7372 and really want to encourage people to set aliases, we'll be more successful if the UX for creating an alias is helpful rather than annoying.

[turt2live]

I think we fixed this with the new alias UX