Add version to outgoing messages

- Added constant for version of release in constants.py
- Added 'v' value representing node's version number in send messages

This version number will help us see what version nodes are running on when diagnosing issues in the future.
Merge pull request #667 from hoffmabc/master

[CRITICAL] Add version to outgoing messages
Add timeout to resolve row lock bug

Simultaneous access to a row when writing and reading will cause an exception. This allows the proces to wait until it's available and then write instead.
Create only one zmq context to reduce overhead

Creating a zmq context for each PeerConnection object is wrong and creates a massive overhead.

Move context creation to parent class
Remove redundant context creation
Fix executable bit check to work on Mac OS X.

* Ignore results from virtualenv folder.
Merge pull request #672 from Renelvon/mac_checkstyle

Fix executable bit check to work on Mac OS X.
Merge pull request #670 from hoffmabc/master

Bug Fixes (single zmq context, timeout in database connection)
update brew installer url
Deactivate bad unused import.

* ebaysdk missing from project requirements.
Enable pylint imports check (F0401).
Do not pylint inside html/bower_components.
Subpackage db and test folders.

* Effectively allows relative imports from/to these folders.
Fix broken imports in the db, features and test packages.
Locally disable import errors.

* Unable to import distutils.utils in Travis CI.
Merge pull request #665 from Renelvon/sane_imports

Install package structure. Fix imports (part 1). Enable pylint flag F0401.
Disallow wildcard imports (W0401).

* Also flag unused names from wildcard imports (W0614).
Refactor wildcard imports.

* Drop wildcard; state imported names explicitly.
* Import each module only once.
* Drop unused imports.
* Fix broken imports: Explicitly import modules
  previously implicitly imported by wildcard.
Merge pull request #673 from Renelvon/no_wildcard_imports

Fix imports (part 2). Disallow wildcard imports (W0401, W0614)
Upgrade to pybitcointools 1.1.15.