SPRINGFIELD — An independent candidate’s fight to run for Congress in central Illinois has been a two-front battle.There’s the legal fight in which the candidate, David M. Gill, argues the number of signatures he needed to collect under law as a third-party candidate is unfair. A lower court judge preliminarily agreed, though a federal appeals panel blocked that opinion.But the Gill campaign is still waiting to see whether the full federal appeals court will vacate the panel’s stay or grant his side …