Fix pdb-related issues

Fix pdb-related issues

In editconf, if a PDB input was read, chain IDs are known, and should
be written if the output is also PDB. This now works again, after
being broken in commit 8dd3c9ae88004054b3.

This required adding missing tpr support to readConfAndAtoms(), which
also fixes that pdb2gmx, insert-molecules, and solvate could not read
tpr files. Those are the only tools that directly or indirectly called
readConfAndAtoms with a .tpr file.

Fixes #2900

Change-Id: I883777be945023a7e69260b22e76df54477828ee