Prop 18: Min deposit param change

Several spam spam proposals have been submitted in the past days (#10 ,#11, #12, #13, #14, #15, #16, #17) and TORI 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 TORI that should be deposited for a governance proposal from 500 TORI to 4000 TORI (~100$ considering a TORI price of 0.03$). 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.