Create a height x 1 drawable instead of a height x width, improving memory usage considerably

We detected that Madvertise was using a lot of memory. Around 4MB, to be more precise, which is very unusual for such a simple library. After using eclipse's MAT, we narrowed it down to this: `sTextBannerBackground`.

Before: ![Before](http://f.cl.ly/items/2b3o2Q3k3q1O0m3w0713/before.png)

We changed this bitmap's width to 1 instead of the width of the display, since we believe it's unnecessary. The results are exactly the same, and this allowed a huge memory usage reduction.

After: ![After](http://cl.ly/2o0x3r2N250l1W173x1w/after.png)