Remove external references to Conformer._E0

In rmgpy/statmech/conformer.pyx, _E0 is the private attribute backing
the public E0 property (to support an Energy cast on setting).
Respect that privacy and use the public interface.
Merge pull request #214 from wking/no-_E0

Remove external references to Conformer._E0

In rmgpy/statmech/conformer.pyx, _E0 is the private attribute backing the
public E0 property (to support an Energy cast on setting). Respect that
privacy and use the public interface.
Corrections to the input file writing.

The solvation writing was just not indented.

There is a default value for the `sensitivityThreshold`,
so if would still print to the input file when `sensitivity`
was not specified. Caused some issues with the website 
input file writing.
QMTP input file writing

Also allows the website input file writer to write
the QMTP block.
Solvation input file writing
Write a liquid reactor if solvent is present

Currently we write `simpleReactor` for everything. Liquid
phase systems need to be run with the 'liquidReactor`
module.