Squashed commit of the following:

commit 48eb4d8839
Author: Syrone Wong <wong.syrone@gmail.com>
Date:   Sun Sep 18 15:46:09 2016 +0800

    Drop useless interface impl

    Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

commit c0a4f3421a
Author: Logan Zhou <xorcererzc@gmail.com>
Date:   Sun Sep 18 00:58:02 2016 +0800

    Revert "Updated to meet the hint from Wongsyrone."

    This reverts commit 84c8053577.

commit 84c8053577
Author: Logan Zhou <xorcererzc@gmail.com>
Date:   Sun Sep 18 00:52:21 2016 +0800

    Updated to meet the hint from Wongsyrone.

commit 333ccb6d1f
Author: Logan Zhou <xorcererzc@gmail.com>
Date:   Sun Sep 18 00:34:52 2016 +0800

    Added duplicate button to config form.

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

- add event handler for KeyDown
- drop unused code, we don't support
  table and rc4 now

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

- Drop redundant code.
  I should read code carefully, mbed TLS will set operation
  when invoking mbedtls_cipher_setkey(), the last param
  const mbedtls_operation_t operation is what we want.
- minor changes

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

* Refine encryption

- Add AES-CTR, blowfish and camellia ciphers

aes-256-ctr
aes-192-ctr
aes-128-ctr
bf-cfb
camellia-128-cfb
camellia-192-cfb
camellia-256-cfb

- Merge the previous PolarSSL and MbedTLS
- Switch to MbedTLS's cipher layer functions
- Add workaround to set cipher operation(encrypt/decrypt)

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

* Add function to get MbedTLS cipher context size

and drop hard-coded ctx sizes

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

ChaCha20 with an extended (96 bit) nonce and a 32-bit counter has
been implemented as crypto_stream_chacha20_ietf() from LibSodium 1.0.4

Please refer to https://tools.ietf.org/html/rfc7539 for details.

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

Now can use esc key to cancel, and don't change focus after change
server from list

Now can use esc key to cancel, and don't change focus after change
server from list

Add a lock on config form to avoid accidental changes