ENH: Support additional path list envvars

Add support for an additional list of environment variables that should
be treated as path lists. Add ability to specify these as lists in the
manner of [Paths] and [LibraryPaths] (which are merged with any values
set in the "traditional" manner for backwards compatibility). Refactor
buildEnvironment to treat PATH and the platform-appropriate library path
in the same manner as these (which greatly simplifies the code).

Besides the added convenience in the configuration file, the generated
wrapper script now also prepends to these variables as well as the usual
PATH and library path variables.
BUG: Don't add '.' to paths via wrapper script

Fix bug in generation of the wrapper script which unconditionally adds
the previous environment paths, resulting in an empty entry (i.e. an
implicit '.') if the variable was not previously set. This avoids a
potential security issue, though it requires using the somewhat esoteric
'${VAR:+:$VAR}' syntax to append the existing value.

This is related to 65531307251f, but affects only the wrapper script, as
opposed to --launcher-dump-environment or the actual launch environment.

Note that this doesn't work on Windows, but since Windows searches the
current directory anyway (at least for PATH), we can live with that for
now.
STYLE: Make ctkAppLauncherConfigure a function

Change ctkAppLauncherConfigure from a macro to a function. This appears
to have no effect on functionality, except that we no longer leak our
local variables into the parent scope (which is good, and the reason to
make the change).
BUG: Fix ctkAppLauncherConfigure dependencies

Change rule to generate the launcher configuration to actually depend on
the input files (i.e. the scripts that contain the configuration files).
This fixes failure to regenerate the configuration when changes are made
at the CMake level.
ENH: Add --launcher-show-set-environment-commands

Add a new option that is somewhere between the existing 'dump
environment' and 'generate wrapper script' options to write (to stdout)
a series of commands to set up the launch environment. This is intended
to be usable like 'eval $(app --launcher-show-set-environment-commands)'
from a POSIX shell in order to modify the caller's environment.

To support this, refactor generateExecWrapperScript to separate out the
common code, which now writes to a QTextStream, and to write directly to
the output script directly (facilitating use of the new method) rather
than to a QStringList.
BUG: Fix quoting of environment variables

Modify generateEnvironmentScript to properly quote environment variables
(introducing a helper method for this purpose) - specifically, to
correctly escape special characters (e.g. quotes, the escaping
character) rather than just blindly slapping quotes around the string -
in order to avoid problems in case a path contains such characters.
STYLE: Avoid gratuitous stack variables

Now that we are using named string literals for our format strings, give
them static storage, as there is no reason to use stack storage for
them.