ticker: Initial support. Closes #466

[bmigunov]

Ticker feature implementation. Added new options, such as: "ticker", "ticker_delimeter", "ticker_interval", "ticker_chars_limit" & "ticker_direction".

"ticker" option enables/disables feature for a given block. "ticker_delimeter" sets a character to separate tail and head of the output string. "ticker_interval" determines the amount of time periods on which the output string is being shifted. "ticker_chars_limit" defines the amount of symbols to be displayed. "ticker_direction" defines the direction in which the characters will shift.

This feature required to add a library to work with UTF8 characters, so now i3blocks has "libutf8proc" in its dependencies.

Closes #466