Make a one jar file monolithic #149

Use tomcat7-maven-plugin to build an executable jar, see target/seyren-web-1.0.0-SNAPSHOT-war-exec.jar.

% java -jar seyren-web-1.0.0-SNAPSHOT-war-exec.jar
...
INFO: Starting Servlet Engine: Apache Tomcat/7.0.37
...
INFO: Starting ProtocolHandler ["http-bio-8080"]

Implementation notes:
- tomcat7-maven-plugin 2.2 does not work
- You can change http port with: jar target/seyren-web-1.0.0-SNAPSHOT-war-exec.jar -httpPort=9090
- tomcat7-maven-plugin creates seyren-web-1.0.0-SNAPSHOT-war-exec.jar but installs seyren-web-1.0.0-SNAPSHOT-exec-war.jar -> wierd
Merge pull request #150 from obazoud/one_jar

Make a one jar file monolithic #149
No longer need jetty runner to execute standalone jar
Executable jar does not open with /seyren context
Use 'GRAPHITE_REFRESH' system property to change the fixed period (in ms) between checks
Merge pull request #152 from obazoud/fixed_period

Use 'GRAPHITE_REFRESH' system property to change the fixed period