Alias-related UI improvements

[tsudoko]

TODO:

• [x] allow setting aliases from the context menu
• [x] make alias change notifications a bit more consistent
• [x] display the alias in the chat window when it's set
• [x] display the alias in the chat header when it's set
• [x] display the alias on the friends list when it's set
• [x] select the alias/name in the input field when using the context menu item (less ambiguous, right now users might get confused and type the alias after the original name) I think it's better the way it is right now
• [x] don't display alias changes for aliases loaded from the metadata file at startup
• [x] enable unsetting the alias
• [x] enable tab completion for /alias
• [ ] enable displaying aliases alongside original friend names as an option

For later (probably not this PR):

• make commands not stay in the input field after executing them
• treat /command␣, /command␣␣ and so on the same way as /command
• display alias/name change notifications differently
• remove empty metadata files? I wouldn't care, but the ~/.config/tox directory is pretty loaded already, perhaps make ~/.config/tox/utox/{transfers,metadata,logs}?

I'm pretty sure there are bugs, I have no idea what I'm doing. Please point out any mistakes.

[GrayHatter]

/alias can also be fixed with #1094

[GrayHatter]

/alias without an following alias should unset it

[GrayHatter]

make commands not stay in the input field after executing them

I think I fixed that in the /sendfile PR #939 , if not It will be in there

[GrayHatter]

@tsudoko "/alias " will unset an alias, but "/alias" will not. if you fix that I'll merge this

no, that's my code. I'll fix it.

[GrayHatter]

merged into develop branch

[GrayHatter]

@tsudoko #1084 is in develop if you wanna roll that into this one?

[GrayHatter]

@tsudoko this is merged into develop in my branch, so I'm closing it here