[nemo-qml-plugin-email] Insert inline image asynchronously when they become available.
[nemo-qml-plugin-email] Build content part strings when possible instead of concatenation.
[nemo-qml-plugin-email] Restore original content if we can't determine the inline part type.
Merge pull request #118 from nemomobile/inlineParts2

[nemo-qml-plugin-email] Insert inline image asynchronously when they bec...