fixed RemoteURL css for CMS issue 1086

Fixed CSS issue with RemoteURL extending past the "Add URL" button text. 

https://github.com/silverstripe/silverstripe-cms/issues/1086

Compiled Compass version 1.0.1

Original Issue example:
![issue1086_original](https://cloud.githubusercontent.com/assets/2508506/4729911/5da012b6-5990-11e4-8e35-7881616e9917.png)

Fixed:
Windows - IE8
![issue1086_fix_win_ie8](https://cloud.githubusercontent.com/assets/2508506/4729912/5da1d3d0-5990-11e4-92b6-690366350006.jpg)

Windows - IE11
![issue1086_fix_win_ie11](https://cloud.githubusercontent.com/assets/2508506/4729908/5d999fd0-5990-11e4-9d54-454a770291e3.jpg)

OSX - Chrome
![issue1086_fix_osx_chrome](https://cloud.githubusercontent.com/assets/2508506/4729910/5d9e4170-5990-11e4-9ca6-8086cd79df65.png)

OSX - Firefox
![issue1086_fix_osx_firefox](https://cloud.githubusercontent.com/assets/2508506/4729913/5da39148-5990-11e4-8631-4c893e745d2b.png)

OSX - Safari
![issue1086_fix_osx_safari](https://cloud.githubusercontent.com/assets/2508506/4729909/5d9cff40-5990-11e4-84ce-21826cb0b454.png)