Clear is allways a replace with spaces and default style
Clean up a bit

Most importantly make sure that screen_datas block container can be a
likned list.

And moved the releaseTextSegment function to the TextStyleLine class
which has to take a Screen which it is suppose to release to. Makes a
bit more sense that way around
make screen_data use std::list

also, count how many lines this screen has ever had

The current screen is allways at the bottom of the total count of lines,
so when a line/block goes out of the current screen, the line number
should not be updated, untill you resize.
First attempt at scrollback...

This is still just in memory, but it should be fairly conservative in
memory useage

++ some smaller fixes I noticed along the way