Added option allowDuplicates

Used to allow users to add the same entry more than once.
Modified addToSelection() and _sortAndTrim methods().
Fixes compatibility with .input-lg, .input-sm

Updated the _render() method to add the bootstrap-specific css classes .input-lg or .input-sm to the main div of the rendered component. Additionally, some minor fixes in the CSS file will handle a few glitches that occur.
Fixes for compatibility with .input-lg, .input-sm

These small fixes are basically just fine-tuning the padding, line-height and margins of some component elements, when the original input fields use the bootstrap-specific .input-lg or .input-sm classes to adjust their size.
Fixes for older glitches (ms-trigger, ms-sel-ctn)

The first out of these two rules reduces the unnecessary left margin of the selection container, causing the selection block to look evenly padded from the top, left and bottom edges of the component.
The second rule fixes a glitch where the trigger covers the top-right and bottom-right rounded corners of the component, while on :hover. It basically shortens the trigger and adds rounded borders to it on hover.
Merge pull request #163 from mjohnson8165/master

Added option allowDuplicates