Development mode for template engine

*Title: Development mode for template engine

*Incentive:
Currently the developer must remove all compiled template files when a source
file has been modified for it to be used in the web page. When all templates
are cleared the system will need to compile them again which takes quite some
time.

*Documentation:
A new INI setting in site.ini has been added, it can be found under the
TemplateSettings group and is called DevelopmentMode. It is disabled by
default and can be enabled by setting.

DevelopmentMode=enabled

After the setting is changed all compiled templates must be cleared, when
they are recreated the code will contain the extra modification checks.

Remember that this setting should not be used on live sites since it performs
extra checking and can make the site slower.