Formalize type attribute and support it in styles

example/style.lua

@@ -0,0 +1,59 @@
+return {
+    short = {
+        height = 48,
+    },
+    toolbar = {
+        style = { 'short' },
+    },
+    toolButton = {
+        align = 'center middle',
+        width = 48,
+    },
+    toolButton_focused = {
+        slices = 'defer',
+    },
+    toolButton_not_hovered = {
+        slices = false,
+    },
+    statusbar = {
+        style = 'panel',
+        align = 'left middle',
+    },
+    listThing = {
+        style = { 'short', 'panel' },
+        align = 'left middle',
+        outline = { 200, 200, 200 },
+        height = 120,
+        padding = 8,
+        background = { 255, 255, 255 },
+        icon = 'icon/32px/Box.png',
+        wrap = true,
+    },
+    dialog = {
+        type = 'submenu',
+        width = 600,
+        height = 400,
+        float = true,
+    },
+    dialogHead = {
+        type = 'panel',
+        height = 40,
+        size = 16,
+        align = 'middle center',
+    },
+    dialogBody = {
+        wrap = true,
+        margin = 4,
+        font = 'font/DejaVuSansMono.ttf',
+    },
+    dialogFoot = {
+        type = 'panel',
+        flow = 'x',
+        height = 40,
+    },
+    dialogButton = {
+        type = 'button',
+        width = 100,
+        margin = 4,
+    }
+}