Implement blur effect

[chregu]

This patch (currently only) implements the blur effect. Maybe useful for some. If anyone likes to add more effects, I'd be happy to integrate them here, before it gets eventually merged.

[leofeyer]

I like the idea and it could help solving contao/core-bundle#1202 (comment) – although we might need to implement the other methods, too.

[ausi]

Looks great, thank you @chregu!

I think we should add some checks here:

1. If the filter attribute is already set, we should append or prepend the blur filter.
2. IDs need to be unique, so we should check that the ID of the filter doesn’t exist already.
3. SVGs can be inlined in HTML, so we should try to use a very unique id (maybe random or some hash).

[chregu]

Totally agree with those 3 points. It was sufficient enough for our needs, but should definitely be extended for common useage

[ausi]

I created a followup pull request: #10

@chregu It would be great if you could take a look if this still generates the desired results for your use case.

[chregu]

@ausi Cool, thanks a lot for the additional work you put into. Works fine on our project with your code.

[Toflar]

@chregu, is that for rokka.io? 😄

[chregu]

@Toflar Sure thing ;)

[ausi]

Merged in f126fca and ba853e2.

Thank you @chregu!

[chregu]

Thank you all for making it better 💛