Make ExportManager::formattedFilename less dependent on member variable states

Add ImageMetaData.h for a standard way to access common image metadata

Make ExportManager::formattedFilename less dependent on member variable states

Part of a set of commits necessary to make this change actually work. They're separate commits for history readability.

Before this change, you have to remember to update everything correctly (e.g., date/time, window title). That was error prone since you needed to keep a lot of context in your head to ensure that you got the correct formatted filename. The data that used to need manual updates must now be passed as arguments.

ExportManager::formattedFilename was made static since member vars are no longer needed internally. It's nicer to do ExportManager::formattedFilename(...) than ExportManager::instance()->formattedFilename(...). This also required a few other functions to be made static with minimal modification.

Keep windowTitle in image metadata

This way it can be passed around without doing anything manually.

Part of a set of commits necessary to make the previous commit actually work. They're separate commits for history readability.

AnnotationDocument: Preserve image metadata

Part of a set of commits necessary to make the previous 2 commits actually work. They're separate commits for history readability.