Added About modal with last commit hash, moved some dialogs to lesionTracker package from viewerbase (OHIF-52)

Packages/viewerbase/client/components/basic/aboutModal/aboutModal.js

@@ -0,0 +1,5 @@
+Template.aboutModal.helpers({
+    githubUrl() {
+        return 'https://github.com/OHIF/Viewers';
+    }
+});