Overlapping dependent phases start time should raise a warning not an error

[nRiccobo]

Logic exists in get_dependency_start_time of the ProjectManager class that raises ValueError if the user specifies a reasonable value. The condition should be replaced with a Warning to notify the user that they specified a value that is not within range, and say why.

Currently, the start time of an installation phase may begin based on some completed percentage of a dependent installation phase. This percentage should be specified between 0.0 and 1.0. However, if the user puts in a value of 1.25 because they wanted the dependent installation phase to start 1.25x after the first installation phase, they will get an error. Furthermore, if the user wants to specify that a phase starts "X days" after another phase, they cannot do this.

Should there be some sort of catch to allow the user to enter the start time based on a percentage of a dependent phase or an integer number of days...