update testng to v6.8.7

- update .iml file
use IntelliJ action infrastructure more consistently

- allows user configuration (e.g. keyboard shortcut)
add plugin version to HTTP user agent
show star icon for starred changes in list

Related to #30
add support for PUT HTTP operations
add action to change starred status of a change

- supported with Gerrit >= 2.8

Resolves #30
Merge remote-tracking branch 'origin/master' into intellij13