add L1Vector.h to the list of installed headers
Bugfix: L1Vector.h was not installed to include/ directory with "make install". Fixes the redmine issue https://lxcbmredmine01.gsi.de/issues/2293
Bugfix: L1Vector.h was not installed to include/ directory with "make install". Fixes the redmine issue https://lxcbmredmine01.gsi.de/issues/2293