Feat: Display name for downloading task

[838]

Adds a option to give the download a readable display name.

For now only used for notification title in android.

[838]

@bartekpacia

Will you please take a look at this when you have time before it falls long behind the master with lots of merge conflicts? :)

[bartekpacia]

Hi @838, thanks for your contribution.

Will you be able to implement the same for iOS? Currently, there's already a lot of Android-specific options and I'd prefer not to make the situation worse.

[838]

Hi @bartekpacia

That was also my intention to add this feature in ios, so the displayName could be used as title instead of filename for the modal dialog when opening a downloaded file. But I saw there is a Swift migration is going on, and therefore I wanted to wait for that to be complete :)