Show the list of children in the commit details (#710)

* feature: add children list to the commit base info view

Useful for navigation between the commits.

* feature: use repository filters to limit children search
* feature: execute children search asynchronously
* feature: respect global commit limit for a good measure
* fix: input lines may contain several commits

The first commit is always the immediate child, so take only 40 initial characters of the line

* fix: hide children behind the preference
* feature: make parents and children scrollable

src/Commands/QueryCommitChildren.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using SourceGit.ViewModels;
+
+namespace SourceGit.Commands
+{
+    public class QueryCommitChildren : Command
+    {
+        public QueryCommitChildren(string repo, string commit, string filters)
+        {
+            WorkingDirectory = repo;
+            Context = repo;
+            _commit = commit;
+            if (string.IsNullOrEmpty(filters))
+                filters = "--all";
+            Args = $"rev-list -{Preference.Instance.MaxHistoryCommits}  --parents {filters} ^{commit}";
+        }
+
+        protected override void OnReadline(string line)
+        {
+            if (line.Contains(_commit))
+                _lines.Add(line.Substring(0, 40));
+        }
+
+        public IEnumerable<string> Result()
+        {
+            Exec();
+            return _lines;
+        }
+
+        private string _commit;
+        private List<string> _lines = new List<string>();
+    }
+}