sptool: sectors extend flags in days/deltas

[magik6k]

• Make --from / --to flags (specifying source sector expiration range) accept delta-from-now (+ prefix), and duration in days (d suffix)
• Make --extension flag accept duration in days (d suffix)
• Add a --no-cc flag which skips CC sector extensions

Example:

$ ./sptool --actor f02620 sectors extend --no-cc --to +90d --extension 200d
skipping sector 5902 because claim 14026049 (client f02034523, piece baga6ea4seaqgtgppncxcotpkcy73ahp4nbdyn75556exrlxsmo3mdr5xjv3a4bi) does not live long enough 
....
skipping sector 5960 because claim 15048764 (client f02034523, piece baga6ea4seaqkba7onklkn4p3yco3sxzkkdvr3yjexbiwl7g67h6rlrjyoju26ka) does not live long enough 
Extending 322 sectors: 
 {
  "Extensions": [
    {
      "Deadline": 0,
      "Partition": 0,
....
      "NewExpiration": 5030398
    },
    {
      "Deadline": 4,
      "Partition": 0,
      "Sectors": "6335,6342,6379,6381-6382",
      "NewExpiration": 5030408
    }
  ]
}
GasLimit: 1.44 G
FeeCap: 48.651 pFIL
MaxFee: 0.06999999961867517 FIL
322 sectors to extended, pass --really-do-it to proceed