Add a new class TerminalStripLayoutPatternXml used to
save / load a TerminalStripLayoutPattern class into a xml.
Also create the namespace QETSVG used to read/write some
svg element / attribute to xml. This class is used by the
class TerminalStripLayoutPatternXml.
Initially it was planned to have separate text configuration for every
terminal level. It's not useful, use same properties for every level is
sufficient and visually more consistent.
By consequent every QVector related to these properties was replaced by
a single value.
TerminalStripLayoutPattern class is now a shared pointer between all
terminal strip item.
QETProject have now a new class : ProjectPropertiesHandler
the goal of this class is to manage every kind of properties used in the
project, this class will be strongly used in future.
