Add New Diagram command with starter templates

- Archify: New Diagram… (Explorer folder menu, File > New File…, Command
  Palette) creates a .archify file from a template and opens the diagram
- Six YAML templates: architecture, workflow, sequence, dataflow,
  lifecycle and an everyday plan; connections carry ids, workflows use
  schema 2
- Title and meta.output follow the file name; template comments are kept
- Tests: every template passes archify validate; integration check for
  the command

Closes #2

templates/architecture.archify

@@ -0,0 +1,50 @@
+# Architecture: the parts of a system and how they connect.
+# Components need a unique id; connections link component ids.
+schema_version: 1
+diagram_type: architecture
+meta:
+  title: Web Application
+  output: architecture.html
+components:
+  - id: users
+    type: external
+    label: Users
+    sublabel: Browser
+    pos: [40, 160]
+    size: [130, 60]
+  - id: api
+    type: backend
+    label: API
+    sublabel: REST service
+    pos: [250, 160]
+    size: [130, 60]
+  - id: cache
+    type: database
+    label: Cache
+    sublabel: Redis
+    pos: [460, 60]
+    size: [130, 60]
+  - id: db
+    type: database
+    label: Database
+    sublabel: PostgreSQL
+    pos: [460, 260]
+    size: [130, 60]
+boundaries:
+  - kind: region
+    label: Production
+    wraps: [api, cache, db]
+connections:
+  - id: users-api
+    from: users
+    to: api
+    label: HTTPS
+    variant: emphasis
+  - id: api-cache
+    from: api
+    to: cache
+    label: read
+  - id: api-db
+    from: api
+    to: db
+    label: SQL