Paste of HTML text removes leading/trailing whitespaces

Even when copying a text within composer with leading or trailing
whitespace, the text is marked as an HTML text in clipboard, and
the whitespace is removed on paste, instead of preserved. The added
code adds whitespaces as necessary.
Skip \n and \r from whitespace recognition on HTML text paste

This fixes a bug in the previous commit. In case of a mutliline
paste the new line markers are properly encoded within HTML tags,
thus adding them as plain text resulted in doubled new lines.
Underline and strikeout lines out of its position in a printout

When printing, the lines for underline and strikeout were placed
out of its position. The was more visible with larger fonts.
Paragraph style drawn incorrectly after font style change

For example, if there is a Header 1 paragraph, and it whole is selected,
and then a bold/italic/underline is changed, then the drawn paragraph
style is like Normal, even the above chooser still shows Header 1. Writing
a new character makes the text drawing fixed, showing the text correctly.

The issue was that HTMLObject's parent change didn't mark the object
properties for recalculation, thus there was used stale style set, calculated
in time when there was no parent set on the object.
Wrong cursor position after paste of text with <div></div>

The <div /> is placed as DISPLAY_BLOCK, which adds one more character
for cursor positioning, which was not counted with, thus after paste
the cursor was positioned before the end of the pasted text.
Bug #699574 - gtk_selection_owner_set() breaks mouse wheel scrolling