Define and use event identifiers

* VuFindSearch/Service.php (EVENT_PRE, EVENT_POST, EVENT_ERROR,
EVENT_RESOLVE): Define constants for event identifiers.
(triggerPre, triggerPost, triggerError, resolve): Use event
identifiers.
Add VuFindSearch event namespace

* VuFindSearch/Service.php (setEventManager): Add `VuFindSearch' event
namespace, following common zf2 pattern.
Simplify lazy-loading new event manager

* VuFindSearch/Service.php (getEventManager): Simplify lazy-loading
new event manager.
Remove unused logger dependency

* VuFindSearch/Service.php ($logger, setLogger, log): Remove unused
logger dependency.
* ../Module.php (setup): Dto.
Use VuFindSearch event namespace

* VuFind/Bootstrapper.php (Bootstrapper): Use VuFindSearch event
  namespace.
Add search system invokable configuration
Remove VuFindSearch service setup functions

* ../Module.php (getServiceConfig, setup): Removed. Service is an
invokable.
Mark CitationTest skipped if short_open_tags is disabled

Mark test skipped if short_open_tag is not enabled. The partial uses
short open tags. This directive is PHP_INI_PERDIR, i.e. can only be
changed via php.ini or a per-directory equivalent. The testCitations()
will fail if the test is run on a system with short_open_tag disabled
in the system-wide php ini-file.
Merge pull request #22 from dmj/t/search-2.1

Minor improvements for release 2.1 (mostly search system related)