Add `tea issues --fields`, allow printing labels #312

refactor the field selection of tea repos ls --fields, so it can be reused with other entities.
use the new generic --fields flag & tableFromItems() to add field selection to tea issues ls & tea ms issues
add more printable fields to issues, most importantly colored labels :) (fixes #268)

Maybe we should reconsider the default fields that are printed for issues. At least labels should be included I think, not sure if we really need author and updated by default

now you use FullName for user, can you add a fiel username witch instead of FullName always use username?

now you use FullName for user, can you add a fiel username witch instead of FullName always use username?

@6543 This actually was the behaviour before too. I added author-id to get just the raw username.

 	}
 	print.IssuesList(issues, ctx.Output)
 	fields, _ := flags.GetFields(cmd, nil)