libgeda: Use sane defaults for "world size".

Adjusts the compiled-in default "world size" to match the default size
used by gschem and gnetlist, etc.

The "world size" determines the area within the schematic plane which
is covered by the "tile" mechanism.  If this area is to small to cover
the schematic, connection tracking silently breaks.  Ed Hennessy
encountered problems when writing the `gsch2pdf' tool because for some
reason junctions weren't being reported correctly by libgeda.

After a very lengthy debugging process, I discovered that the default
"world size" compiled into libgeda was much smaller than that used by
gschem etc., and that most schematics were falling outside it, thus
breaking connection tracking and causing the "missing junction"
symptom.

This interim patch adjusts the default compiled in world size so that
libgeda (mostly) DTRT.  In the future, this should be fixed properly
by using R-trees or a similar structure for spatial lookups in libgeda
rather than the rather inflexible "tile" mechanism.
Remove papersizes.h files, which are no longer used.
gsch2pdf: Use eda_renderer_draw_cues().

Removes gsch2pdf's own junction tracking system and uses libgeda's
instead.  This wasn't done sooner because of the issue fixed in commit
e8d8b02af8cd.
Notify on locked items deletion

User can choose to delete:
1. All selected locked and non locked items
2. Only non locked selected items
3. Nothing (cancel)

Closes-bug: lp-1027596
libgeda: Clarify difference between rc and config files.

Rewrite doc comments to make it clear that "rc" files are Scheme init
files, as opposed to configuration files (EdaConfig).
libgeda: Try to load standard configuration files.

Make calls to RC file loading functions also trigger attempts to load
the associated configuration files, on a best-effort basis.  Since
it's not a major problem if config files can't be loaded (that's what
defaults are for) ignore missing config files and just log a warning
when a load fails for other reasons.

When an RC file is being loaded, the appropriate configuration context
is made available via the (rc-config) function.
gaf: Add `gaf config' command.
gaf-config: Don't warn if config file doesn't exist.

It's valid for config files to not exist (ideally the defaults should
be good enough for everybody).
libgeda: eda_config_get_context_for_path() should always succeed.

If it's possible for the configuration system to fail to return a
context for a path then using the API can be hasslesome.  We maybe
should change how the configuration filename for bogus paths is
chosen, and probably add some warning messages, but it makes sense for
eda_config_get_context_for_path() to always return a configuration
context of some description.
Add Scheme scripts and macros for replacing deprecated config.

This stuff couldn't be added as modules because the rc-config function
isn't available to code in modules (for various reasons).  Some way of
addressing this issue probably ought to be found at some point
gschem: Port printing-related configuration to new config system.
gschem: Initialise compiled-in configuration on startup.

Some configuration items require built-in default values.  Provide an
i_vars_init_gschem_defaults() function to provide this.