Prop 27: Increase min deposit param

Huge amount of spam/scam proposals have been submitted in the past day and MNTL price currently allows to spam the chain with fake proposals very cheapy. We have decided to propose the community to increase the min amount of MNTL that should be deposited for a governance proposal from 512 MNTL to 50000 MNTL (~350$ considering a MNTL price of 0.0069$). This should make it less likely for bad actors to create scam or spam proposals in the future, preserving the real meaning of on-chain governance.