Hotfix/samm spider

[Antsega]

First class in crawler successfully scrapes pdfs from: https://samm.dsca.mil/listing/chapters
Second class in crawler successfully scrapes pdfs from: https://samm.dsca.mil/policy-memoranda/PolicyMemoList-All , with specific exclusions

Tested locally using shell

 $env:PYTHONPATH = "$(Get-Location)"
 $CRAWLER_DATA_ROOT = "./test-samm"
New-Item -ItemType Directory -Force -Path $CRAWLER_DATA_ROOT| Out-Null
$prevManifestFile = Join-Path $CRAWLER_DATA_ROOT "pre-manifest.json"
New-Item -ItemType File -Force -Path $prevManifestFile | Out-Null
$sammSpider = "dataPipelines/gc_scrapy/gc_scrapy/unfinished/samm_spider.py"    
$outputFile = Join-Path $CRAWLER_DATA_ROOT "output.json"
scrapy runspider $sammSpider `
-a download_output_dir=$CRAWLER_DATA_ROOT `
-a previous_manifest_location=$prevManifestFile `
-o $outputFile

Ripped the @static method from stigg_spider; open to refactoring this method to match desired outcome for naming convention