Use custom layout for ACRA report dialog, not default one.

Styling the default dialog was difficult and it doesn't obey some of the guidelines provided by the Android design docs:

https://www.google.com/design/spec/components/dialogs.html#dialogs-specs (see "Content Guidelines")

This change introduces a custom dialog extending the base ACRA reporting activity. Specifically, it introduces a padding of 24dp around the dialog contents.

I couldn't find design specs on the specific spacing between different elements within the dialog, so I used the same spacing of 20dp suggested to use between the title and the main body of the dialog.

At the very least, this change should make it easier to update styles in the future if somebody suggests improvements to the layout of the dialog.

Before

After