Major Update: fmincon, streamline code

Moved all code in "Euler's Method" folder to "Tumor Data" folder --> no
need to switch between folders every time

Deleted myODEfunc1.m and myODEfunc2.m (code is now part of comments in
costFunction.m)

costFunction
- Enhanced readability
- Better comments
- only x is counted towards cost
- now takes s0 as an initial guess
- no longer needs s_data as an argument

euler3.m is the shortest, most concise Euler's Method code. It has the
same output as MATLAB's built-in ode solvers (i.e. ode45). See the
docstring and comments in euler3.m for more information

fminconScript is a script (not a function) used to run fmincon, a
constrained function optimization solver (compared to fminsearch, an
unconstrained optimization solver).
- nonlconstr.m specifies a non-linear constraint implemented by fmincon

LoopThetaInitial
- not really necessary anymore if we use fmincon
- Due to high sensitivity of fminsearch to initial guesses
(theta_initial), we wanted to systematically loop fminsearch through a
range of initial guesses.
- sometimes throws an error when fminsearch tries values for parameters
that are unstable --> instead should use fmincon to apply constraints

ode.m
- uses ode45 to numerically solve system of differential equations
specified in simulODE.m
- created to test accuracy of Euler's Method (euler2 and euler3) and to
quickly evaluate s(t) and x(t) for given values of v,p,h,s0

simulODE.m
- contains system of differential equations
- note: feedback on p now depends on x*(1-s)

simulODErad.m
- same as simulODE.m but adds effects of radiation therapy (feedback on
p now depends on # of (nonstem cells + dying cells))