ui: Added custom trail dialog (issue #249)

* open custom trail dialg via button in top of trail controls
* search from symbol to symbol or all referenced/referencing of symbol
* define search depth with slider
* define horizontal/vertical layout
* define node and edge types
* renamed depth graph to trail in graph ui
* added custom trail UI tests

fortune cookie message = A happy surprise is waiting for you.

testing/graph_view/graph_view_tests.srctrlprj

@@ -7,6 +7,7 @@ Test Suites:\n\n
 [::\tmOVERVIEW_TESTS\ts\tp]\n
 [::\tmLAYOUT_TESTS\ts\tp]\n
 [::\tmDEPTH_GRAPH_TESTS\ts\tp]\n
+[::\tmCUSTOM_TRAIL_TESTS\ts\tp]\n
 [::\tmGROUPING_TESTS\ts\tp]\n
     </description>
     <source_groups>
@@ -37,5 +38,5 @@ Test Suites:\n\n
             <type>C++ Source Group</type>
         </source_group_475571d1-b082-4fff-81c5-d099c19f957d>
     </source_groups>
-    <version>7</version>
+    <version>8</version>
 </config>