upgrade mail plugin from v0.9.1 to v1.0.0

- fix mail port bug (https://github.com/nforge/yobi/issues/575)
sbt: add dependency graph plugin

- see https://github.com/jrudolph/sbt-dependency-graph
Merge branch 'dep-graph' of kjkmadness/yobi

from pull request 905
Merge branch 'patch/mail-plugin' of kjkmadness/yobi

from pull request 902