Verb for adding dependencies to package.xml and CMakeLists.txt

Simple verb to add a package dependency to the 4 locations in a catkin package:

```
<run_depend></run_depend>
<build_depend></build_depend>
```

And to CMakeLists.txt

## Usage

```
roscd YOUR_PACKAGE_TO_MODIFY
catkin depend dep1 [dep2 [dep3...]]]
```

## Current Limitations

 - ~~You don't mind loosing the blanks of your package.xml~~
 - ~~You don't mind the deps being added to the bottom of package.xml~~
 - 'find_package(catkin REQUIRED COMPONENTS' must be on the same line
 - Does not check for already existing deps in CMakeLists.txt (but it does in package.xml)                                                                  
 - Assumes you have at least one <build_depend> and <run_depend> already added, does not error if not

These are all pretty easy to fix, I just should be working on something else right now