Support set cursor style (DECSCUSR)

[Tyriar]

We should support the following CSI code to allow more fine-grained control of the cursor and also allow configuration via .bashrc (eg. adding echo -e "\e[5 q" for blinking bar)

CSI Ps SP q
          Set cursor style (DECSCUSR, VT520).
            Ps = 0  -> blinking block.
            Ps = 1  -> blinking block (default).
            Ps = 2  -> steady block.
            Ps = 3  -> blinking underline.
            Ps = 4  -> steady underline.
            Ps = 5  -> blinking bar (xterm).
            Ps = 6  -> steady bar (xterm).

Both xterm and gnome-terminal support this out of the box. This can be done after the Parser refactor is complete #462.

[Tyriar]

Tyriar@1a67893 implements this, will wait until parser refactor #462 is merged before creating PR though.