Add experimental option "--web"

1. When `--web` is selected, Jetty will start up on 8080 and open the
   user's web browser to a webpage
2. Using some shady, unreliable classpath querying, we initialize a
   class that's responsible for running the JAR that's currently being
   executed
3. The user is presented with a web page, displaying *all* rules, with a
   check box next to every rule. The user can choose which rules to run,
   and which directory to run on.
4. When the user selects rules and a directory, then presses "enter", a
   report iframe is generated.
Fix build
Rename to .java
Clean interaction between index and HtmlReportExecutor

Conflicts:
	src/main/java/com/selesse/jxlint/web/HtmlReportExecutor.java
Remove redundant Gradle dependency
Add "initializeForWeb" to ProgramSettings
Add better error handling for reading report
Update CHANGELOG