__data_empty_label when 0 targets to chart.

Code to place the chosen __data_empty_label in the center of the main chart when 0 targets supplied. Takes into account sub chart being active.
Styling has been moved to c3.css
Merge branch 'patch-3' of https://github.com/bjlbernal/c3 into bjlbernal-patch-3
Fix typo for mimeType - #236
Set default for data.x_format - #268
Suggested changes made

Good catch. <code>init()</code> is now only defining the <code>text</code> tag in the main chart. I've moved the setting of the <code>x</code> and <code>y</code> into <code>redraw()</code> along with the label text. <code>x</code> and <code>y</code> are using <code>width</code> and <code>height</code> instead of calculating <code>(getCurrentWidth() - margin.left - margin.right)</code> as before. Indentation corrected as well, so Travis CI shouldn't error out on that either.
add cusom name support
Fix nan of label for arc
Fix legend position when flush() called
Merge branch 'patch-3' of https://github.com/bjlbernal/c3 into bjlbernal-patch-3
Fix empty text when no data to show - #275
Fix conflict
Merge pull request #282 from iphands/master

add cusom name support
Add data.keys for filter input data - #283
Remove toXXX API and add transform() instead
Add sample for empty data
Add 'length' and 'to' options to flow - #207
Add color API - #263
Merge branch 'master' of github.com:masayuki0812/c3
Fix conflict
Fix flow when no grids