Small improvements on the mining page UX

- INDEXING_BLOCKS_AMOUNT = 0 disable indexing, INDEXING_BLOCKS_AMOUNT = -1 indexes everything
- Show only available timespan in the mining page according to available datas
- Change default INDEXING_BLOCKS_AMOUNT to 1100

Don't use unfiltered mysql user input

Enable http cache header for mining pools (1 min)

backend/mempool-config.sample.json

@@ -12,6 +12,7 @@
     "BLOCK_WEIGHT_UNITS": 4000000,
     "INITIAL_BLOCKS_AMOUNT": 8,
     "MEMPOOL_BLOCKS_AMOUNT": 8,
+    "INDEXING_BLOCKS_AMOUNT": 1100,
     "PRICE_FEED_UPDATE_INTERVAL": 3600,
     "USE_SECOND_NODE_FOR_MINFEE": false,
     "EXTERNAL_ASSETS": [