Initial Working Version on Alsa Policy-Policy-Hook

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+Alsa-Hook-Plugin
+
+Object: Provide a Hook on Alsa PCM to check permission again AGL Advance Audio Agent
+Status: Working Proof of Concept
+Author: Fulup Ar Foll fulup@iot.bzh
+Date  : August-2017
+
+Functionalities:
+ - Execute a set of websocket RPC request again AGL binders to allow/deny access
+ - Keep websocket open in an idepandant thread on order to monitor event receive from AGL audio agent 
+
+Installation
+ - Alsaplugins are typically search in /usr/share/alsa-lib. Nevertheless a full path might be given
+ - This plugin implement a hook on a slave PCM. Typically this slave PCM is a dedicated virtual channel (eg: navigation, emergency,...)
+ - Config should be place in ~/.asoundrc (see config sample in PROJECT_ROOT/conf.d/alsa)
+
+Config
+```
+# Define sharelib location and entry point
+# -----------------------------------------
+pcm_hook_type.MyHookPlugin {
+    install "AlsaInstallHook" 
+    lib "/home/fulup/Workspace/AGL-AppFW/audio-bindings-dev/build/Alsa-Plugin/Alsa-Hook-Callback/alsa_hook_cb.so"
+}
+
+# Create PCM HOOK with corresponding request calls to AGL Audio Agent
+# --------------------------------------------------------------------
+pcm.MyNavigationHook {
+    type hooks
+    slave.pcm "MyMixerPCM" # Target PCM to effectively play sound 
+
+    # Call request that should succeed before accessing slave PCM
+    hooks.0 {
+        type "MyHookPlugin"   # Name=xxxx should match with pcm_hook_type.xxxx
+        hook_args {
+
+            # URI to AGL-Advance-Audio-Agent binder
+            uri   "ws://localhost:1234/api?token='audio-agent-token'"
+
+            # Call request to send to binder (initial label is free, query is optional)
+            request {
+                MyFirstCheck {
+                    api   "alsacore"
+                    verb  "ping"
+                } 
+                MySecondCheck {
+                    api   "alsacore"
+                    verb  "ucmset"
+                    query "{'devid':'hw:v1340','verb':'Navigation','dev':'speakers'}"
+                }    
+            }
+        }
+    }
+}
+
+```
+
+NOTE: 
+
+* Hook plugin is loaded by Alsa libasound within player context. It inherits client process attributes, as UID/GID or
+the SMACK label on AGL. This smack label is tested by AGL security framework when requested a call on the audio-agent binder.
+As a result the call will only succeed it the permission attached the application in Cynara matches. 
+
+* Hook plugin keep a connection with the Audio-Agent until PCM is closed by the application. This connection allow the
+Audio-Agent to send events. eg: pause, quit, mute, ...
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