Restructure CLAMP documentation tree

Restructured and refactored the CLAMP documentation
- Introduced a hierarchical structure to the documentaiton
- Added a tree for builtin and TOSCA CLAMP
- Cleaned up formatting
- Added documentation for participants
- Added placeholders for missing particioant, control loop runtime,
  and control loop GUI documentation
- Fixed some hanging references

Issue-ID: POLICY-3363
Change-Id: I3933be08af3984f2bb4e08707a8c5b5b454f540c
Signed-off-by: liamfallon <liam.fallon@est.tech>
diff --git a/docs/clamp/controlloop/design-impl/participants/participant-intermediary.rst b/docs/clamp/controlloop/design-impl/participants/participant-intermediary.rst
new file mode 100644
index 0000000..7f6cf49
--- /dev/null
+++ b/docs/clamp/controlloop/design-impl/participants/participant-intermediary.rst
@@ -0,0 +1,13 @@
+.. This work is licensed under a Creative Commons Attribution 4.0 International License.
+
+.. _clamp-controlloop-participant-intermediary:
+
+Participant Intermediary
+########################
+
+The CLAMP Participant Intermediary is a common library in ONAP, which does common message and
+state handling for participant implementations. It provides a Java API, which participant
+implementations implement to receive and send messages to the CLAMP runtime and to handle
+Control Loop Element state.
+
+.. warning:: To be completed