Implement a basic version of users' profile fly-out menu

[joausaga]

Implement a fly-out menu following the design presented here and having these functionalities:
1- Display the name and username of the user;
2- Have a button that allows users to log out of the system. The session of the user should be deleted after he/she logs out of the system. After the logout, the user should be redirected to the login page;
3- Have a menu with two options: one to access to the user profile information and another to access the configurations of the system. When the user clicks on these options the vuejs modal should be displayed. For the basic version of the menu, the content of the modal can be empty.

[joausaga]

@Ana-Cris: next things TODO in this issue
1- It is not clear that clicking on the avatar makes a menu to be displayed. We need to add a visual clue that indicates that the picture is an interactive feature of the system. See, for example, the arrow (visual clue) on the right side of the picture in the top menu of Github.
2- Change the title of modal according to the name of the option selected.

[Ana-Cris]

Implementation:

1- Display the name and username of the user

To implement this funcionality a Get Request was added to the API (Backend.vue). The output is the list of users. This list is used in the function DisplayName() in Header.vue. The function compares each username in the list with the username of the Logged in user.

2- Allow log out of the system

The logout () function in Header.vue nulls the content of the variables Backend.username and the Backend.token that saves the user's token. Then the user is redirected to the Login page.

3- Vue.js Modal

The Modal.vue file is the template of the Modal.
It was created two functions: one to open the Modal and another to close it. (openModal (id) and closeModal() in Header.vue). The parameter "id" allows identify the title of the Modal, if the user clicks on "Settings" or "My Profile" buttons.