Fix zoom and pan issues (fix:#2 fix:#3)

[nopnop]

Hi @mephux, @nemoguardx and @bumbu, this is a PR about issue #2 (and maybe #3 too).

Maybe, you should use a less "square" layout (for both nodes and canvas) to test this plugin: some of the inconsistency are hidden when the layout is very a square (because this is a very specific case).

Here is an illustration:

• nerite/1 - The current implementation
• nerite/2 - With this fix

Based on @mephux illustration :

• volageta/1 - The current implementation
• volageta/9 - With this fix

[djcas9]

@nopnop awesome work man!

[bumbu]

@nopnop Thanks a lot.

[nopnop]

You are welcome, Thanks to you: this plugin is usefull!