Cut long text into multiple DL at start

Bug 5763685

To improve performance, preventively cut the the into display
list of 3-10 lines of text. Further updates to small parts of
the text (such as adding an underline on a word) will only
invalidate and redraw the affected sub display list.

DLs are aligned with paragraphs, just like they will be during
text edition.

Change-Id: I0d60debc7fdaea8b29080a6eacb2d60205e7d547