Rename the bases from construct_smooth_data

[boyiguo1]

Currently, the "design matrix" returned from contruct_smooth_data are named in the pattern var_name.baseX. However, such a naming convention doesn't help to distinguish the null space from the penalized space, which creates more problems during variable/function selection.

The naming convention should be a combination of var_name.nullX and var_name.penX. It also helps with creating groups.

[boyiguo1]

Fixed as suggested. See commit 900b4d1