feat(wm): add dynamic layout selection rules

This commit adds a new feature which allows the user to specify a set of
rules for a specific workspace that will be used to calculate which
layout to apply to that workspace at any given time.

The rule consists of a usize, which identifies the threshold of window
containers which need to be visible on the workspace to activate the
rule, and a layout, which will be applied to the workspace when the rule
is activated.

Both default and custom layouts can be used in workspace layout rules.

When a workspace has layout rules in effect, manually changing the
layout will not work again until the rules for that workspace have been
cleared.

This feature came about after trying but failing to modify the custom
layout code in such a way that the width percentage of a primary column
in a custom layout might be propagated to the fallback columnar layout
when the tertiary column threshold is not met.

Although this new feature introduces more complexity, it is strictly
opt-in and can be completely ignored if the user has no interest in
adjusting layouts based on the visible window count.

re #121

komorebi-core/src/lib.rs

@@ -86,6 +86,9 @@ pub enum SocketMessage {
     WorkspaceName(usize, usize, String),
     WorkspaceLayout(usize, usize, DefaultLayout),
     WorkspaceLayoutCustom(usize, usize, PathBuf),
+    WorkspaceLayoutRule(usize, usize, usize, DefaultLayout),
+    WorkspaceLayoutCustomRule(usize, usize, usize, PathBuf),
+    ClearWorkspaceLayoutRules(usize, usize),
     // Configuration
     ReloadConfiguration,
     WatchConfiguration(bool),