Added FlatProjectView. Used it to create an 'All Issues' project in pit-swing.

Solves issue #11: pit-swing: Add a default, "all-projects" view.

libpit/src/com/jdbernard/pit/FlatProjectView.groovy

@@ -0,0 +1,34 @@
+package com.jdbernard.pit;
+
+public class FlatProjectView extends Project {
+
+    public FlatProjectView(String name) { super(name); }
+
+    public Issue createNewIssue(Map options) {
+        throw new UnsupportedOperationException("The FlatProjectView is " +
+            "read-only.")
+    }
+
+    public Project createNewProject(String name) {
+        throw new UnsupportedOperationException("The FlatProjectView is " +
+            "read-only.")
+    }
+
+    public boolean delete() { return true };
+
+    public void eachIssue(Filter filter = null, Closure closure) {
+        def sorter = filter?.issueSorter ?: Filter.defaultIssueSorter
+        def gatherIssues
+        def gatheredIssues = []
+
+        gatherIssues = { project, f -> 
+            project.eachIssue(f) { gatheredIssues << it };
+            project.eachProject(f) { gatherIssues(it, f) }
+        }
+        for (p in projects.values()) 
+            if (!filter || filter.accept(p))
+                gatherIssues(p, filter)
+
+        gatheredIssues.sort(sorter).each(closure)
+    }
+}