use JavaMail as a replacement for parseDateStr

[tomholub]

part of #1051

Please see if there is any readily available date parsing library for email in Java that behaves similarly and passes our tests. If there is, please use it.

[DenBond7]

@tomholub

javascript has a "magic" date parser we use that we'll need in Kotlin. Maybe some mail library has this (we use it to parse email headers)

If we are going to use JavaMail to work with MIME messages we don't need to port parseDateStr to Kotlin. JavaMail does it himself

[DenBond7]

#1058

[DenBond7]

@tomholub Could you clarify where we use parseDateStr? I see usage in flowcrypt-android.js only.

[tomholub]

If you don't use it, then you can skip this.