plug-ins: port colormap-remap to GEGL
plug-ins: add loading and saving of the image's resolution in file-pcx
Bug 711241 - Broken or unknown metadata tag should not cancel...

...the whole metadata loading

Don't serialize a value that does not UTF-8-validate to XML. This is
not a real fix, but no matter what we do here in the future, UTF-8
validation should always be part of the serialization, in order to
avoid passing broken data into the core.
libgimpbase: use gexiv2_metadata_get_exif_tag_rational() to get the resolution

and remove our own rational parser, we can get it back from git if we
need it again.
libgimpbase: fix gimp_metadata_set_resolution() to only set rationals

Rationals have integers as nominator and denominator, so we can't set
something like "300.5/1". Instead, multiply the nominator and
denominator of non-integer ppi values until the error is smaller than
0.01, or the denomiator reaches 100 ("300.5/1" becomes "601/2").
plug-ins: only include "libgimp/gimp.h" and "libgimp/gimpui.h"
devel-docs: change the libgimpwidgets doc stuff so it handles GEGL types
app: also include <gegl.h> when we include "libgimpwidgets/gimpwidgets.h"
libgimp: also include <gegl.h> when we include "libgimpwidgets/gimpwidgets.h"
modules: also include <gegl.h> when we include "libgimpwidgets/gimpwidgets.h
libgimpwidgets: include <gegl.h> in all files that include gimpcolordisplay.h
libgimpwidgets: add GimpColorDisplay::convert_buffer()

which takes a GeglBuffer and a GeglRectangle.
app: port gimp_display_shell_render() to GimpColorDisplay::convert_buffer()

which means applying a series of nops until the display filters are
ported.
build/win: Start building libgexiv2 and exiv2
modules: implement convert_buffer() in the high contrast display filter
modules: implement convert_buffer() in the gamma display filter
modules: implement convert_buffer() in the lcms display filter
app: variable renaming in gimpdisplayshell-render.c for better readability
modules: implement convert_buffer() in the color blind display filter
modules: remove the old convert_surface() from gamma and high contrast