feature #10547 [Admin] Remove avatar (Tomanhez)

This PR was merged into the 1.4-dev branch.

Discussion
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| Q               | A
| --------------- | -----
| Branch?         | master
| Bug fix?        | no
| New feature?    | yes
| BC breaks?      | no
| Deprecations?   | no
| License         | MIT

**When admin doesn't have avatar:**
![Screenshot 2019-07-25 at 14 47 42](https://user-images.githubusercontent.com/39232096/61875586-40d8ac00-aeeb-11e9-8bc1-db26a463bd47.png)

**When avatar is added:**
![Screenshot 2019-07-24 at 09 22 50](https://user-images.githubusercontent.com/39232096/61773596-55d31380-adf5-11e9-96e4-700686f91df2.png)

**After removing avatar:**
![Screenshot 2019-07-25 at 14 47 42](https://user-images.githubusercontent.com/39232096/61875586-40d8ac00-aeeb-11e9-8bc1-db26a463bd47.png)


Commits
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e0d1973b63ba9f2ba205d9c3c80501a2b226701c Add behat test
29cb485a8d7ce2ce7b70f8effbd16a80a1620cb8 Add context and element
f4f84eaa5ca0b5f0463020be8001923698098724 Add delete avatar in js site
69f81b91658cff29d81ccc91053bd85847becb0a Add repository and controller
b76dbb6df6791f24b5f2fc451bf09b158f4d8f61 Add form
6e731fb269ad1ced645871bc59935daa07457c10 fixes