ListWidget with more capabilities: add/remove/modification

[m-vdb]

Hi @jschrewe,

In our project, we needed the ListField(FileField) structure to have more capabilities:

• allow removal of elements (the current code is buggy)
• have a better widget to allow removal + modification

I did some work on our fork to have this possibility, you can find it here: Work4Labs#8.

Some comments about what I did:

• commits are not atomic, I used a trial / error approach
• the code is not factorised as wanted, I didn't want to change your code too much
• there are no tests (reason for number 1)

We are relying on this project a lot in our production environment, and I'm wondering several things: how active is your repo? Do you still use your code in production environment? Would you be inclined to let me be a contributor of the project? Can we setup tests (circleci / travis / other?) ?

Let me know what you think, I'm open for a quick chat :)

[m-vdb]

cc @olivierlefloch