Improved sorting of datatables [Fixes #357]

[cjchirag7]

Fixes #357
The following changes have been made :

• Modified the comparator function to return -1, +1 or 0, depending upon the comparison of the elements
• If the values can be converted to number, then they would be first converted to number, and then the comparison would occur. Currently, the comparison, was done, taking them all, as strings, in lexicographical order. But there might be some cases like : '2' > '12' (lexicographically) but 2 < 12 (numerically) , which may produce undesired results to the user.
• Made the cursor to a 👆 , when user hovers over the up/down button
• Increased the size of up and down buttons from 10px to 15px, so that they are visible
• Now, the sort works perfectly, in both Chrome and Firefox

[birm]

Thanks!