Implement bottom up validation

[akhilkumarpilli]

Fixes: #345

[colin-axner]

LGTM, great work!

[anilcse]

lgtm, just small nits

[anilcse]

Let's re-order this check

Suggested change

	if err = c.ValidatePathEnd(p.Src); err != nil {
	return err
	}
	if p.Src.Version == "" {
	return fmt.Errorf("source must specify a version")
	}
	if p.Src.Version == "" {
	return fmt.Errorf("source must specify a version")
	}
	if err = c.ValidatePathEnd(p.Src); err != nil {
	return err
	}

[anilcse]

I think if the ClientID is nil, there's no point in validating connection or channel details. We can just return err if the ClientID is nil and connectionID is not nil. Similarly for ChannelID

Suggested change

	if pe.ClientID != "" {
	if err := c.ValidateClient(chain, height, pe); err != nil {
	return err
	}
	}
	if pe.ConnectionID != "" {
	if err := c.ValidateConnection(chain, height, pe); err != nil {
	return err
	}
	}
	if pe.ChannelID != "" {
	if err := c.ValidateChannel(chain, height, pe); err != nil {
	return err
	}
	}
	if pe.ClientID != "" {
	if err := c.ValidateClient(chain, height, pe); err != nil {
	return err
	}
	if pe.ConnectionID != "" {
	if err := c.ValidateConnection(chain, height, pe); err != nil {
	return err
	}
	if pe.ChannelID != "" {
	if err := c.ValidateChannel(chain, height, pe); err != nil {
	return err
	}
	}
	}
	}
	if pe.ClientID == "" && pe.ConnectionID != "" {
	return fmt.Errorf("ClientID is not conifgured for the connection: %s", pe.ConnectionID)
	}