GUAC-914: Migrate to logback and latest SLF4J. Read logback.xml from GUACAMOLE_HOME if present.
GUAC-916: Release ALL keys when browser window loses focus.
GUAC-915: Clean up all log messages within Guacamole.
Merge branch 'master' into GUAC-546

Conflicts:
	guacamole/src/main/java/org/glyptodon/guacamole/net/basic/AuthenticatingFilter.java
	guacamole/src/main/java/org/glyptodon/guacamole/net/basic/BasicGuacamoleTunnelServlet.java
	guacamole/src/main/java/org/glyptodon/guacamole/net/basic/BasicLogin.java
	guacamole/src/main/java/org/glyptodon/guacamole/net/basic/RestrictedFilter.java
	guacamole/src/main/java/org/glyptodon/guacamole/net/basic/RestrictedHttpServlet.java
	guacamole/src/main/java/org/glyptodon/guacamole/net/basic/crud/protocols/List.java
	guacamole/src/main/java/org/glyptodon/guacamole/net/basic/websocket/WebSocketSupportLoader.java
	guacamole/src/main/webapp/WEB-INF/web.xml
	guacamole/src/main/webapp/scripts/client-ui.js