RTS-GMLC fixes

[bknueven]

Summary/Motivation:

Fixes a few issues I found attempting to run 5-minute RTS-GMLC with Prescient

Changes proposed in this PR:

• Minor fixes to the RTS-GMLC parser
• Make reserves.csv optional for RTS-GMLC parser
• Fixing bug with PowerGeneratedT0 and startup/shutdown curves introduced in Startup/shutdown curve #219
• Adding flag and only optionally enforcing shared reserve ramping constraints (and adding optional flag for current baselines)
• Forcing a warmstart in the lazy PTDF solve loop. Helps the performance of solvers which don't carry the prior integer solution over automatically between solves.

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