Add grouping options menu

We need a way to customize the command grouping:

```proto
// CommandTree is a path to a hierarchy of command tree nodes.
// Resolves to a service.CommandTree.
message CommandTree {
// The capture to get the tree for.
Capture capture = 1;
// The command filter used to create the tree.
CommandFilter filter = 2;
// If true then commands will be grouped by API.
bool group_by_api = 3;
// If true then commands will be grouped by context.
bool group_by_context = 4;
// If true then commands will be grouped by thread.
bool group_by_thread = 5;
// If true then commands will be grouped by draw calls.
bool group_by_draw_call = 6;
// If true then commands will be grouped by frame.
bool group_by_frame = 7;
// If true then commands will be grouped by user markers.
bool group_by_user_markers = 8;
// If true and grouping by context, 'no context' groups will be created.
bool include_no_context_groups = 9;
// If true and grouping by frames, commands after the last frame will be
// grouped into an 'incomplete frame' group. Only if there is at least one
// complete frame.
bool allow_incomplete_frame = 10;
// If positive, synthetic sub-nodes are created for nodes with more than
// this many children.
int32 max_children = 11;
}
```

Some captures just don't group nicely with the defaults.