Show error messages to user

[canbax]

In lots of places, we print logs to the console with console.log or console.error. The user can not see this. Let's just pop out a message. It might be a status message or a pop-up or both.

[canbax]

Testing all these error messages are cumbersome.

• Some messages are actually never to be seen but in the future somehow could happen.
• Some of them could easily be tested such as the "Use Title Posters" content menu item. One image has a false URL so we show a message.
• A error modal will be shown if a false URL is presented. This can be tested by going to URL http://visuall.herokuapp.com/?URL=https://raw.githubusercontent.com/herencalik/testfile/master/visuall.txt and simply going to another non-existing URL.
• Loading a random JSON file for showing in the canvas should show an error.
• An error will be shown if Neo4j database is down or the Internet connection is down.

[ugurdogrusoz]

Review of error/warning messages:

• Make sure all modal dialog titles are simple and uppercased. Examples: "database query execution error" or "Database query execution error" -> "Database Query Execution Error", "Background image" -> "Background Image", "Invalid query!" -> "Invalid Query"
• "Load JSON", "Can NOT process JSON string" -> "Load", "Cannot process provided JSON file!", "Database returns erronous result" -> "Database Query"
• "Image URL", "Image url is falsy: Error: Network Error" -> "Use Title Poster", "Poster(s) does not exist!" (also do this on the context menu of Title - when trying to shown poster of a single title)
• "Graph is empty", "Empty response from database!" -> "Empty Graph", "Empty response from database!"
• "Timebar", "rangeMaxDate or rangeMinDate is falsy!" -> "Timebar", "range bounds are incorrect!"