Add neural network ( perceptron )

Update documentation

Add support of SQL Server

Fixes in bar graph, line graph, box plot.

Adapt for Electron v0.35.6 API

Properly terminate the application when the window is closed

Add possibility to get a png image of a graph

When loading from BigQuery, check is job is complete

Fix bugs in histograms.

Improve box plot representation.

Add localization of help files.

Allow multi-line sql query when loading data from mysql

Detect numerical fields when importing from mysql.

Can copy from spreadsheet to clipboard with ctrl-C or cmd-C