Merge pull request #39 from nemomobile/vdv-devel

[nemo-qml-plugin-email] Add attachmentModel.
Merge pull request #40 from nemomobile/vdv-devel

[nemo-qml-plugin-email] Save attachments to temporary file after download
Merge pull request #41 from nemomobile/vdv-devel

Change Idle state to NotDownloaded.
[nemo-qml-plugin-email] Add exportUpdates invokable.