Fixes issue #501

Added direction checking for abstract features
fixes #503

allow any feature as endppint of a feature connection.
Added DMS to the supported scheduling protocols property
Fixed directionality problems in unit tests.  This was needed as a
result of 49cabdf5feedc305579953de728424fe73e5caf1.
ensure that EMFIndexRetrieval onl returns NamedElements.
Find duplicates again, except for AADL_Project
Revert "fixes #503"

This reverts commit 5002e789a56d64754b9b9cbce7ea30be49bfe5a2.
Merge pull request #502 from philip-alldredge/develop

Icon updates for use by the graphical editor.