LP#1449709: caching compiled Template Toolkit templates

LP#1449709: caching compiled Template Toolkit templates

This patch enables caching of compiled Template Toolkit
files on Evergreen web servers, which can provide a modest
improvement in the time it takes (say) TPAC to render
a page, particularly by a fresh Apache backend.

This is controlled by a new Apache virtualhost variable,
OILSWebCompiledTemplateCache, which can be set to a
directory on the webserver for storing compiled templates. This
is enabled by default for new installations.

This patch also adds OILSWebTemplateStatTTL, which can be
use to tweak the STAT_TTL Template Toolkit setting. Note this
bit anticipates future work to also cache TT objects, so
at the moment, setting OILSWebTemplateStatTTL has little effect.

Finally, this patch also fixes a bug where attempting to
disable OILSWebDebugTemplate would result in internal server errors;
it also sets the default value of this setting to false.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>