Improved taxonomy by supporting tags, multiple terms allowed, and required kind of vocabulary for specific content type.

Updated node web form, to support taxonomy editing if allowed (specific support for CMS_VOCABULARY.is_tags: BOOLEAN).
Added notion of required or optional module dependencies.

examples/demo/site/modules/taxonomy/scripts/install.sql

@@ -0,0 +1,24 @@
+
+CREATE TABLE taxonomy_term (
+  `tid`	INTEGER NOT NULL PRIMARY KEY AUTO_INCREMENT UNIQUE,
+  `text` VARCHAR(255) NOT NULL,
+  `weight` INTEGER,
+  `description` TEXT,  
+  `langcode` VARCHAR(12)
+);
+
+CREATE TABLE taxonomy_hierarchy (
+  `tid`	INTEGER NOT NULL,
+  `parent` INTEGER,
+  CONSTRAINT PK_tid_parent PRIMARY KEY (tid,parent)
+);
+
+/* Associate tid with unique (type,entity)
+ * for instance: "page" + "$nid" -> "tid"
+ */
+CREATE TABLE taxonomy_index (
+  `tid`	INTEGER NOT NULL,
+  `entity`	VARCHAR(255),
+  `type` VARCHAR(255) NOT NULL,
+  CONSTRAINT PK_tid_entity_type PRIMARY KEY (tid,entity,type)
+);