Resources: Add retry and retry delay meta parameters

All resources can now set a retry limit (-1 for infinite) and a delay
between retries. This applies to both the CheckApply methods, and the
Watch methods as well. They each have their own separate counts, but use
the same input meta param, since I decided it wouldn't be useful to have
a separate watchRetry and watchDelay set of meta parameters.

In the process, we got rid of about 15 error cases which would normally
panic.

This patch required a slight overhaul of the Event system.

The previous commit is an earlier version of this patch which I decided
to leave in to "show my work" as I used to have to do in math class.
It's slightly more correct with the current event system, and this
version is less correct and has a few bugs, but that is because the
event system needs a massive overhaul, and once that's done this should
all work properly for the corner cases.

examples/file3.yaml

@@ -0,0 +1,14 @@
+---
+graph: mygraph
+comment: You can test Watch and CheckApply failures with chmod ugo-r and chmod ugo-w.
+resources:
+  file:
+  - name: file1
+    path: "/tmp/mgmt/f1"
+    meta:
+      retry: 3
+      delay: 5000
+    content: |
+      i am f1
+    state: exists
+edges: []