Yammer initial integration
Added configuration setter from the plugin

 * Bump version
remove yammer install in init block
honor stealth flag
set plugin name
add is_configured? method just like other plugins do

 * remove initialize
simplify abort run
use configure_options!
remove post install message
rewrite get_access_token
Merge remote-tracking branch 'upstream/master'
bump yammer dependency
revert caching yammer client
create attachment first
Use attachment1 as opts for image stream
simpler comment
move retries in constant - assign its value to local var instead of modifying it
Merge remote-tracking branch 'upstream/master'
comply to RuboCop offenses
miss encoding requirement