Xml users bug 918

# Xml users bug 918

Add functionality to present user name in dropdown box as well as user avatar (if available).

Prepared functionality to pull new users data (`xml file`) from web. Such functionality can by triggered as crone job.

### Scope of this pull request:

 - js code to remove char if user is not selected
 - js code to show avatar
 - lxml iter parsing for users data
 - add tests to secure new implementation
 - add lib requests to get new data from web server (via GET request)

### Tests:

 - add tests to secure new implementation (with super fancy mocking)
 - coverage 100% (see below)

### Usage:

run app: `$ ./bin/flask-ctl debug fg`

### Gist:
- no pep8 issues
- coverage:

```
Name                        Stmts   Miss  Cover   Missing
---------------------------------------------------------
presence_analyzer               3      0   100%   
presence_analyzer.helpers      29      0   100%   
presence_analyzer.main          3      0   100%   
presence_analyzer.utils        41      0   100%   
presence_analyzer.views        54      0   100%   
---------------------------------------------------------
TOTAL                         130      0   100%   
----------------------------------------------------------------------
Ran 18 tests in 0.158s

```