Emojis: Wait for the first letter before showing the emojis popup

[MightyCreak]

Right now, as soon as we hit : the emojis list pops up. But some time we just really want to write : as in:

Example: this is a valid colon.

or

Check the list below:

• one
• two

The GitHub behavior is that if there is a letter just before the colon, then the popup doesn't show.
Personally, I think it's pretty useless to show the popup as soon as : is written. I think the rule should be:

If there is no letter before `:` and at least one letter after:
    Show the emoji popup filtered with the letter(s) after the `:`

[MightyCreak]

In slack it even waits for the second letter to be written (but personally I don't like it).

Edit: I think they wait for the second letter so that the popup doesn't show when writing text smileys like :) :-) :D :P.
Personal opinion: I still think one letter is enough, especially since there are no emoji starting with ) or -, or even with an upper case letter if we really want to be pedantic.

[MightyCreak]

Part of #2984

[Peque]

As of 1.9.0 I think this may be implemented. At least, I need to type 2 characters to see the pop-over emoji suggestion list.

[aaronraimist]

I agree