Improve charts responsiveness

[AndreaBarbasso]

I'm submitting a ... (check one with "x")

[x] bug report => Search github for a similar issue or PR before submitting
[ ] feature request => Please check if request is not on the roadmap already https://github.com/primefaces/primeng/wiki/Roadmap
[ ] support request => Please do not submit support request here, instead see http://forum.primefaces.org/viewforum.php?f=35

Plunkr Case (Bug Reports)
No need to have a plunker, just look at Ultima's Charts page.

Current behavior
If you collapse the left-hand menu charts are not drawn again in their new size, as they only traslate position. This is a breaking behaviour when they should reduce size.

This is easily achieavable by setting the canvas wrapper position as relative as seen on chartjs docs.

Expected behavior
Charts should follow their parent's resizing.

Minimal reproduction of the problem with instructions

• Go on Ultima's Charts page, resize menu, look at charts staying the same.
• Go to any other page, change menu type to Overlay.
• Go back to Charts page, change menu back to static. Look at charts overflowing.

[AndreaBarbasso]

I wanted to set up a PR with the given fix, though it's not enough. If resizing is done with an animation, the performance is horrible.