improve error handling

- show more meaningful messages in connection test dialog
- cleanup method signatures (remove IOException where possible)

Fixes #4
optimize imports
fix coding style
Merge remote-tracking branch 'remotes/origin/master' into features/file-comments

Conflicts:
	src/main/java/com/urswolfer/intellij/plugin/gerrit/rest/GerritApiUtil.java
	src/main/java/com/urswolfer/intellij/plugin/gerrit/rest/GerritUtil.java
add support for file based comments (view and add)

- Gerrit 2.7 or newer is required for viewing comments

Resolves #3

Merge remote-tracking branch 'features/file-comments'
Changing of main panel view - default showing only open changes from current project