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

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testing/graph_view/data/custom_trail_tests.cpp

@@ -0,0 +1,85 @@
+
+#define CUSTOM_TRAIL_TESTS
+
+#include "custom_trail_files/custom.h"
+
+// TEST: open and close dialog
+// START ----------------------------------------------------------------------
+
+// ACTION 1: Click on custom trail button in graph
+// RESULT 1: dialog opens on top of window
+
+// ACTION 2: Close with click on Cancel
+// RESULT 2: dialog closes
+
+// ACTION 3: Use custom trail shortcut Ctrl + L
+// RESULT 3: dialog opens on top of window
+
+// ACTION 4: click on main window
+// ACTION 5: open again
+// RESULT 5: dialog opens on top of window
+
+// ACTION 6: press ESC
+// RESULT 6: dialog closes
+
+// END ------------------------------------------------------------------------
+
+
+// TEST: from -> to
+// START ----------------------------------------------------------------------
+
+// ACTION 1: search from "CustomD"
+// ACTION 2: search to int
+// ACTION 3: select infinite depth
+// ACTION 4: select horizontal layout
+// ACTION 5: select all node and edge types
+// Action 6: click search
+
+// RESULTS 6:
+// - Graph shows multiple paths
+// - Graph contains: CustomD -> CustomB, CustomC -> CustomA -> func -> int
+
+// Action 7: Repeat search with:
+// - select vertical layout
+// - uncheck node field
+
+// RESULTS 7:
+// - Graph one call chain to func
+// - Graph goes top to bottom
+// - Graph contains: CustomD -> CustomB -> CustomA, func2 -> func -> int
+
+// END ------------------------------------------------------------------------
+
+
+// TEST: from -> all referenced
+// START ----------------------------------------------------------------------
+
+// ACTION 1: search from "CustomD::c"
+// ACTION 2: select all referenced
+// ACTION 3: select depth 3
+// ACTION 4: select horizontal layout
+// ACTION 5: select all node and edge types
+// Action 6: click search
+
+// RESULTS 6:
+// - Graph shows multiple paths
+// - Graph contains: CustomD -> CustomC -> int, char, bool, func2, CustomA
+
+// END ------------------------------------------------------------------------
+
+
+// TEST: from <- all referencing
+// START ----------------------------------------------------------------------
+
+// ACTION 1: search from "func"
+// ACTION 2: select all referencing
+// ACTION 3: select depth infinite
+// ACTION 4: select horizontal layout
+// ACTION 5: select all node and edge types
+// Action 6: click search
+
+// RESULTS 6:
+// - Graph shows multiple paths
+// - Graph contains: CustomB, CustomC -> CustomA, func2 -> func
+
+// END ------------------------------------------------------------------------