refactor(errmsg): refactor error messages

[christianlangevin]

• Use lower case for all error messages
• Remove leading spaces from error messages
• Remove ***ERROR prefix from error messages
• Close Inconsistent use of store_error() #758

Example of program output when an error is encountered in the list reader:

Using Simulation name file: mfsim.nam

    Solving:  Stress period:     1    Time step:     1

ERROR REPORT:

  1. Error reading list. The number of records encountered exceeds the
     maximum number of records. Number of records found is 2 but MAXBOUND is
     1. Try increasing MAXBOUND for this list. Error occurred reading the
     following line: 
     >>> 1 1 2     -10.00000000

UNIT ERROR REPORT:

  1. Error occurred while reading file 'gwf_ats01a.wel'

[mjreno]

Looks good @langevin-usgs, like the standardization.