Merge pull request #35 from nemomobile/vdv-devel

[nemo-qml-plugin-email] Improve accounts model signals.
Merge pull request #36 from nemomobile/vdv-devel

Add back signals removed by mistake in last commit.
Merge pull request #37 from nemomobile/vdv-devel

[nemo-qml-plugin-email] Filter out disabled accounts from accounts list ...
[nemo-qml-plugin-email] Modified message body to behave as proper QML property
Merge pull request #38 from antseppa/master

[nemo-qml-plugin-email] Modified message body to behave as proper QML pr...
[nemo-qml-plugin-email] Don't allow send html email.

More modifications are needed in order to support this.
[nemo-qml-plugin-email] Add attachmentModel.

Improve attachment download.