bug in FAKE colvar affecting sum hills
Fixed outfile in case of no communicator
retrieve the bias from outside
Metad: read an external potential

At variance with EXTERNAL,
this bias is used when calculating the WT hills height
Added framework to use driver on multiple trajectories

I adapted the debug replica exchange stuff. Since running on multiple
trajectory could be useful, I leave --multi as a non-hidden option.

I slightly changed behavior of the hidden flag --debug-grex (now one sets the exchange stride, not the number of replicas - the latter is set with --multi). Thus, a couple of retests had to be updated
Added MW cite and docs
Fixed make install with static
Added "has" tools

Added more ways to check if tools are installed. Now also
plumed --has-matheval
is allowed
Improved conditional execution of regtests
Added regtest for MATHEVAL

regtest is executed only if plumed --has-matheval
--has-almost option flag in driver
CS2BACKBONE first regtest (scalar)
CS2BACKBONE AVERAGING test
data folder for CS2BACKBONE
updated regtest gitignore
Fixed permissions upon install

Permissions of installed files were not correct. Now after
install all permissions are reset so that "group" and "others"
can read and execute everything
Merge branch 'v2.0'