Print: add method to convert profile to grayscale

(experimental)

Add the method PrintLayout::convertPixmapToGrayscale()
to convert a rendered profile pixmap to grayscale.
It will probably be faster to have
ProfileGraphicsView render in grayscale under certain
conditions (and use a specific color table) instead -
e.g.:

ProfileGraphicsView::setPrintMode(bool printMode,
	bool useGrayScale);

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Profile: add the isGrayscale flag

setPrintMode() can now be used to set the
profile to be plotted in grayscale.

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Print: pass grayscale flag to setPrintMode()

We pass the value of 'color_selected' stored in the
print options to ProfileGraphicsView::setPrintMode().
This way the profile can be printed in grayscale
internally instead of converting a QPixmap to
grayscale.

There are a couple of questions here:
1) Are all the 'if/then' checks for all individual
colors faster than the direct QPixmap/QImage grayscale
coversation.
2) The direct grayscale conversation does not give
control of individual colors, but can it look actually
better?

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Profile: support grayscale plotting

This patch adds the getColor() helper function to
ProfileGraphicsView and EventItem so that retrieving
a certain color can depend on a 'isGrayscale' flag.
This flag is private and only set by
ProfileGraphicsView::setPrintMode() at this point.
EventItem also now accepts 'grayscale' as a constructor
argument.

A couple of side modifications are:
- move setBackgroundBrush() to ProfileGraphicsView::plot()
- set the same pen color as brush color for the dot in the
'!' symbol inside EventItem::EventItem().

TODO: look for color issues when printing using the
custom grayscale table

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Colors: a couple of grayscale color tweaks

change the B/W color (index 1) of some of the
colors - e.g. BACKGROUND, ALERT_FG.

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>