Add '--no-fallback-messages' flag to silence fallback messages

[lambdalisue]

Currently, fallback messages are always shown when the lemonade server is down.

I understand that it is quite important to tell what happens to the users. However, I often found that the messages are bit annoying, especially when I use lemonade as a clipboard program of neovim by manually assign g:clipboard.

So I added '--no-fallback-messages' flag to silence this warning like:

    $ echo 'hello' | pbcopy

    $ ./lemonade paste --host="127.0.0.1" --no-fallback-messages
    hello

    $ ./lemonade paste --host="127.0.0.1"
    2018/01/24 06:05:37 dial tcp 127.0.0.1:2489: getsockopt: connection refused
    2018/01/24 06:05:37 Fall back to localhost
    hello

This commit fixes #27

[pocke]

Thank you for your pull-request. The feature is reasonable to me. But I have not maintained Lemonade (see. https://github.com/pocke/lemonade/issues/25 ), so I don't have a plan that is reviewing this pull-request. If someone reviews and approves, I'll merge this pull-request. Or I'll review it but I cannot do soon.

[lambdalisue]

Fair enough. I wait 👍

[raa0121]

[pocke]

@lambdalisue @raa0121 Thank you!