Implement shouldUpdate to avoid unnecessary component remounts

[abdyer]

I based this on the implementation for ImageSpec in the Litho repo. It's debatable which props should be included in the check, but hopefully this helps others avoid the image flicker I issue I ran into.

[pavlospt]

@abdyer The conversation on this issue with Andy Street involved the isPureRender=true as well. Isn't that needed anymore?

[abdyer]

@pavlospt Thanks for the reminder. I had it in my working code, but we're not using this library directly so I forgot to include it here. Added.

[pavlospt]

@abdyer Great!

[charbgr]

Thanks @abdyer ! Looks good to me! I will merge it but I will not upload an artifact due to some bintray issues I face. I will try to solve them on the weekend! Maybe it will require to change the package name to solve the issue(maybe: com.github.charbgr:litho-picasso2:1.0)

I am also thinking of bumping the litho version and upload then the artifact.
What do you think @pavlospt @abdyer?

[pavlospt]

@charbgr yeap bumping the version as well would be nice!

[charbgr]

Friendly ping.. It is up under com.github.charbgr:litho-picassox:1.0 and with AndroidX support! :) @pavlospt @abdyer

Thanks @abdyer for the contribution!