1) import with updating index entries instead of replacing existing index file
2) atomic replace support for darwin platform

added feature to export and import data into fdb

1. Fix: Failed to get json data from pack on asset update.
2. Fix: Failed to get content-type from meta data.

1. FIx: Normal bucket operations

fix: normal bucket write- data append instead of overwriting

1. Fix: Failed to get saved json data on Update/Upsert media

1. Fix: Media not created with provided recordID. No data found to update.
2. Fix: Invalid infile index in memory on save operation.

1. Fix: "requiredData" not updated in index file

1. Add: Enable FDB security for Pack and Mixed Bucket

1. Add: Required data on get asset in header.
2. Fix: Update and delete operations for normal bucket.

update: updating lazywrite interval
modification:removing unnecessary files 

1. Fix: Asset not saved to mixed bucket due to extra index field "name".
2: Fix: Failed to get saved asset due to missing "rowID" in index.

1, Fix: File is being used by another process error on atomic write. Closed temporary file conditionally,

* added encryption support in fdb 
* added feature of dynamic encryption key generation function

* removed unused code
* added lock for reading pack file

moved packfile related functions in filemdl and done changes in fdb accordingly

1. Fix: Atomic file not updated, Hard link issue.
2. Add: Create temp directory if not present at app root.

const changed to var due to build issues on windows

FDB changes for reindex, filepack, fast read and write changes

added reindexing feature in fdb,
added filepack module,
modification in filemdl module