PAINTROID-299 Refactor SaveImageAsync, CreateFileAsync

[CodeChamp-SS]

Files that were refactored:

1. SaveImageAsync
2. CreateFileAsync
3. MainActivityInteractor
4. MenuFileActivityIntegrationTest
5. OraFileFormatIntegrationTest

Replaced AsyncTask with Coroutines in SaveImageAsync and CreateFileAsync classes, and renamed them to SaveImage, CreateFile respectively. Added runBlocking to the respective test usages of these files in MenuFileActivityIntegrationTest and OraFileFormatIntegrationTest classes.

https://jira.catrob.at/browse/PAINTROID-299

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