Update EncryptedContactStore to not use deprecated/removed methods

The PGPEncryptedDataGenerator constructor and addMethod calls used in
EncryptedContactStore were deprecated in version 1.49 and removed in
version 1.51 of Bouncycastle.

Update the calls to use the recommended non-deprecated versions.

Change-Id: I134fd8c0b4538ae23a2c17dd0a632ddaff28aa3d
Bump Bouncycastle version to 1.51

This version fixed some bugs [1] and latest SSHD release that we need
has upgraded to this version as well: [2].

[1] https://www.bouncycastle.org/releasenotes.html
[2] https://issues.apache.org/jira/browse/SSHD-362

Change-Id: I84aee1e620091bcd49a1f0be47f4da011a8ff3ee
Bump SSHD Mina version to 2.0.8

SSHD version 0.13.0 uses this Mina version.

Change-Id: I7e27dce435764a19aa27b58ea619d063f640a8fb
SSHD: Update to 0.13.0

Long standing exhausting thread pool SSHD bug was apparently fixed
upstream [1].

All Gerrit releases since 2.8.5 are known to suffer from this problem
with the consequence that Gerrit must be restarted overnight.

[1] https://issues.apache.org/jira/browse/SSHD-348

Change-Id: Ic52277050aa0cd19b19531ee997d312fd7273ebc
Merge changes from topic 'sshd-upgrade' into stable-2.9

* changes:
  SSHD: Update to 0.13.0
  Bump SSHD Mina version to 2.0.8
  Bump Bouncycastle version to 1.51
  Update EncryptedContactStore to not use deprecated/removed methods