Observation App - Changed file names, Marker Popup redifined 

**Files name changed to App name :**
- ```observation_view.py```  -- to --  ```observation.py```
- ```observation_url.py```  -- to --  ```observation.py```
- ```observations.html```  -- to --  ```observation.html```

**Implemented ```edited_by``` field in action :**
- Previously ```edited_by``` field was containing only creator of marker.
- But now it's pushing new members into edited_by field.

**Major changes in Marker Popup interface (of landing page) :**
- Changed UI of marker popup.
- Now hyperlinks in the *Description*/*Observation note* will be clickable.
- Added *Contributed by* field in popup
- Will show *Edited by* field when there exist more than one editor of same marker.

**Added *Contributor name* field and validation in Marker input fields :**
- Now validation has been put to fill all the input fields.
- Also for anonymous user there will be visibility of field name - *Contributor Name*.
- Sensitivity of save/edit button improved. (Depends on change of content in popup input fields).

**Provided hyperlink to *Observations* text in Left panel**
- So that user can redirect to landing page.