for in the PresetCollection: The 1st preset is always the "-- default --"
even if there are some presets starting with an ASCII character lower than '-'.
https://github.com/prusa3d/Slic3r/issues/603
thanks @lordofhyphens, https://github.com/alexrj/Slic3r/pull/3275
Improved handling of custom G-code blocks: Slic3r will try to extract
the target extruder and bed temperatures from the custom G-code blocks.
The incompatible presets are hidden in the tabs if show_incompatible_presets
is false. If show_incompatible_presets is true, there is a button to
show / hide the incompatible presets from the tab selector.
The values of StaticPrintConfig derived objects were searched by a name
walking through a huge chained if.
Now they are being mapped with a std::map.
Also initialization of StaticPrintConfig classes from their ConfigOptionDef
defaults is done by maintaining a single global definition of each
StaticPrintConfig derived class, and a new instance is initialized
from this static copy.
Also the ConfigOption instances are casted using static_cast
wherever possible, and their types are verified by a virtual type() method.
This approach avoids insiginificant performance penalty of a dynamic_cast.
Also the compare and clone methods were added to ConfigOption,
and the cloning & compare work on binary values, not by serialization.
