OilProps Viscosity-at-temperature needs to take into account the max viscosity based on pour point.
Some oil records did not have any pour point information.
So we need to account for this.
Some oils have associated Kinematic viscosities without a reference temperature.  We need to handle that.
added custom command to reinstall_oil_lib so user can easily install
latest if oil_library has been updated. Usage and tests:
  python setup.py resinstall_oil_lib
  py.test --pyargs oil_library
Trac_516, Trac_623
- removed halflife from OilProps

Added/changed OilProps attributes
- changed mass_components to mass_fraction and added placeholders for
  other properties like boiling_point, mw (molecular_weight)
  - assumes boiling_point is 'inf' for resins and asphaltenes
  - molecular weight is only defined for saturates/aromatics
** again these are placeholders and will need to update and add tests
Density calculation in OilProps needs to follow Adios density calculation method.
(WIP) Trac_623 - added HalfLifeWeatherer
- removed half_life data_arrays since they are not time varying or
  varying per LE. Made this a property of HalfLifeWeatherer. Needs more
  work but focus on evaporation for now
- removed InitHalfLivesFromOilProps

Trac_624
- weather_elements works like get_move and returns the remaining mass at
  end of time_step. The model updates 'mass' and 'mass_components' arrays

Trac_516
- since number of components will depend on the data, ElementType
  updates the mass_components ArrayType based on 'num_pc' attribute of
  'OilProps' object. ElementType().substance contains OilProps object
updated tests with changes in commit fb4fff
- marked some tests in test_weatherer with xfail
  - need to decide/resolve Trac_626 before updating these tests
The new get_density method in OilProps was breaking the unit tests.
added a minimum version number for SQLAlchemy >= 0.9.1 else it fails
during runtime
fixed computation of exponential decay
(WIP) Trac_516 - added evaporation module
Trac_628: added environment variables as dict for now
(WIP) Trac_516
- added 'density' data_array, changed InitMassComponentsFromOilProps
  to InitArraysFromOilProps(). Currently, it initializes 'mass',
  'mass_components', 'density'
Merge branch 'master' of https://trac.orr.noaa.gov/git/PyGnome into evaporate
For the boiling point calculation in OilProps, we try to get the oil api first, otherwise we determine the api from the reference densities.
added some notes to Location Files that will need changes when they are put into WebGnome