build: turn off travis ci email notifications; add slack notification (encrypted)
build: turn off travis ci email notifications; add slack notification (encrypted)

musicEnfanthen/Knora,nie-ine/Knora,dhlab-basel/Knora,nie-ine/Knora,dhlab-basel/Knora,dhlab-basel/Knora,musicEnfanthen/Knora,musicEnfanthen/Knora,musicEnfanthen/Knora,dhlab-basel/Knora,dhlab-basel/Knora,nie-ine/Knora,musicEnfanthen/Knora,dhlab-basel/Knora,musicEnfanthen/Knora,nie-ine/Knora,musicEnfanthen/Knora,dhlab-basel/Knora,nie-ine/Knora,nie-ine/Knora