Make tags separator configurable

A B C. 10 aastat tagasi uuendaja Alex Jenter 10 aastat tagasi 0
Allow users to choose which character will function as tag separator instead of having space as the only option, so that we can have tags with spaces. E.g., define comma (",") as tag separator and allow tags to have space in them, like this:

tag 1,this is all tag 2,and all these words here belong to tag 3

organizing complexity:medium tags