Add `beforeDraw` and `afterDraw` hooks to the annotations

[stockiNail]

This PR is adding before/after draw hooks in order to allow the user to apply whatever needed customization on out-of the-box annotations. Fix #146.

The hooks will be invoked once for every annotation for each drawing cycle.

plugins: {
  annotation: {
    annotations: {
      line: {
        type: 'line',
        ....
        beforeDraw(context) {
          console.log('beforeDraw');
        },
        afterDraw(context) {
          console.log('afterDraw');
        },
      },
    }
  }
}

Hook	Arguments	Return type	Default	Description
beforeDraw	context	void	annotation.beforeDraw	invoked before the element drawing
afterDraw	context	void	annotation.afterDraw	invoked after the element drawing

Common hooks for all annotations can be set in the annotation plugin options:

plugins: {
  annotation: {
    beforeDraw(context) {
      console.log('Common beforeDraw');
    },
    afterDraw(context) {
      console.log('Common afterDraw');
    },
    annotations: {
      line: {
        type: 'line',
        ....
      },
    }
  }
}

TODO

• [x] test cases
• [x] types
• [x] documentation
• [x] samples