update core js - keyCacheWipe, key_mismatch fix, plainAtt data

[tomholub]

This PR updates core functionality by adding a keyCacheWipe endpoint (useful when wiping pass phrase which was kept in memory) and ensuring that a mismatched message keys properly reports key_mismatch error even when missing a pass phrase.

Also plainAtt blocks are no longer filtered out of the response, so that they can be rendered / their content is can be downloaded for #194

issue #197

---

Tests (delete all except exactly one):

• Tests updated here https://github.com/FlowCrypt/flowcrypt-mobile-core/pull/157

---

To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[tomholub]

discussion at FlowCrypt/flowcrypt-android#1251 (comment)

[tomholub]

@ekievsky or @Kharchevskyi please have a look that the app still works as expected and if so, approve or add comments. Thanks!

[Kharchevskyi]

Tested on update-core branch and also by pulling in feature/issue-197-pass-phrase-memory. Functionality works fine

[tomholub]

@Kharchevskyi then you can go to Files changed -> Review changes -> Approve and that will merge the PR. Thanks!