Change Non-Functional Requirement (NFR) labels in the SRS to be consistent with the template

[BilalM04]

This issue is a result of issue #3753

Currently, the NFR labels are inconsistent between examples. For some examples, the NFR labels end in "-able". Ex. maintainable, understandable, usable, etc. While for others, it ends in "-ability". Ex. maintainability, understandability, usability, etc.

Change the all the NFR labels to be consistent with the Smith et al SRS template. This means we should be using the labels ending in "-ability".

Change Should be made in the following examples:

• [ ] dblpend
• [ ] GlassBR
• [ ] SWHSNoPCM
• [ ] PDController
• [ ] Projectile
• [ ] SglPend
• [ ] SSP
• [ ] SWHS