Fix problem with messages loading

[kadavr95]

Currently VK loads only 100 messages per request instead of 1500., which leads to missing of 14/15 of all messages (can be verified by opening Google Chrome Developer Tools > Application > WebSQL and checking ids of messages in the database, which would be in pattern 1-100, 1500-1600, 3000-3100 and so on).

Fix implements simple reducing of messages amount extension expects to get from VK, so it would load them in batches by 100, instead of 1500, thus requesting all of them, although slowly.

[TimmyChannel]

@kadavr95 Дай бог тебе здоровья, добрый барин)