Updates to string output of generated channel info

e.g.
     Gates:
        gate m:
            instances: 3
            forward rate: 1000 * (v - (-0.04))/0.01 / ( 1 - exp(-(v -
(-0.04)) / 0.01))
            reverse rate: 4000 * exp((v - (-0.06))/-0.02)
        gate h:
            instances: 1
            forward rate: 70 * exp((v - (-0.06))/-0.02)
            reverse rate: 1000 /(1 + exp((v - (-0.04))/0.01))

@adrianq unfortunately the strings used in InfoTreeCreatorTest.java
needs to be updated every time the structure of the generated string is
updated, but the error output from that class is helpful for finding the
exact line to update.