Add hooks support

[mfuentesg]

The idea behind this feature is, add the ability to execute commands before/after some specific tasks on this plugin. i.e: after upgrade, before upload.

Constraints:

• [ ] Must be configurable (maybe in Sync Settings.sublime-settings file)

  Sync Settings.sublime-settings

  {
  "hooks": {
  "before_upgrade": [
  {
  "command": "my_custom_command",
  "args": {
  "foo": "bar"
  }
  }
  ]
  }
  }

• [ ] Must be written as sublime text plugins

import sublime
import sublime_plugin

class ExampleCommand(sublime_plugin.TextCommand):
    def run(self, edit):
        self.view.insert(edit, 0, "Hello, World!")