make bootstrap optional even when bootstrap samples exist

This pull-request adds a flag to matrixfit, computefps and fit.effectivemass allowing the user to forego bootstrapping the fit (or decay constant computation respectively), even if the correlation function is bootstrapped and bootstrap samples are used to estimate the VarCov matrix for the effectivemass fit. The reason for this  is a particular use-case when performing many fits to check for fit range dependence. Since the error information from the bootstrap is not strictly necessary in that case, disabling it allows for substantial time savings. Of course the default setting is to bootstrap the fit!

In addition for fit.effectivemass, this adds chisqr and Qval to the return value to be consistent with matrixfit.