improve ssl certificate handling

- enable HttpClientBuilder#useSystemProperties() for better integration with IntelliJ certificate manager
- remove manual setup of PoolingHttpClientConnectionManager (better handled by HttpClientBuilder)
- add support for certificates that are signed by an untrusted authority and are not self signed - thanks to Jordan Armstrong for the hint

Related to issue #55
major refactoring of rest access

- remove IntelliJ dependencies in rest access

Related to issue #56
major refactoring of rest access

- move code to package com.urswolfer.gerrit.client.rest

Related to issue #56
add basic example code for rest client
add copy of parts of com.google.gerrit.extensions

- disabled parts of ActionInfo
additions to com.google.gerrit.extensions

- parts which are required for plugin implementation
port rest client to com.google.gerrit.extensions api

Related to issue #56
add guice provider for GerritApi

- minor cleanups
fix listing changes for currently open projects only
pass auth-data to http-client-builder-extensions

- when testing a new connection, the inected auth-data (from settings) may be outdated
adopt to recent changes in Gerrit extensions-api

Related to issue #56
adopt to recent changes in Gerrit extensions-api

- minor refactorings in client code

Related to issue #56
adopt to recent changes in Gerrit extensions-api

Related to issue #56
bump version to v0.8.0-SNAPSHOT
fix handling when Gerrit url and git remote url are not equal

Resolves #64
display project name in update notification
add support for range comments

Resolves #66
bump version to v0.8.0