Collect resource names from a data frame

## Examples

```
pathways <- import_omnipath_interactions()
resources_in(pathways)
#> [1] "ACSN" "ACSN_SignaLink3"
#> [3] "ARN" "Adhesome"
#> [5] "AlzPathway" "BEL-Large-Corpus_ProtMapper"
#> [7] "Baccin2019" "BioGRID"
#> [9] "CA1" "CancerCellMap"
#> [11] "CellCall" "CellChatDB"
#> [13] "CellChatDB-cofactors" "CellPhoneDB"
#> [15] "CellPhoneDB_Cellinker" "CellTalkDB"
#> [17] "Cellinker" "Cui2007"
#> [19] "DEPOD" "DIP"
#> [21] "DLRP_Cellinker" "DLRP_talklr"
#> [23] "DOMINO" "DeathDomain"
#> [25] "ELM" "EMBRACE"
#> [27] "Fantom5_LRdb" "Guide2Pharma"
#> [29] "Guide2Pharma_Cellinker" "Guide2Pharma_LRdb"
#> [31] "Guide2Pharma_talklr" "HPMR"
#> [33] "HPMR_Cellinker" "HPMR_LRdb"
#> [35] "HPMR_talklr" "HPRD"
#> [37] "HPRD-phos" "HPRD_KEA"
#> [39] "HPRD_LRdb" "HPRD_MIMP"
#> [41] "HPRD_talklr" "HuRI"
#> [43] "ICELLNET" "InnateDB"
#> [45] "InnateDB_SignaLink3" "IntAct"
#> [47] "KEA" "KEGG-MEDICUS"
#> [49] "Kinexus_KEA" "Kirouac2010"
#> [51] "LRdb" "Li2012"
#> [53] "Lit-BM-17" "MIMP"
#> [55] "MPPI" "Macrophage"
#> [57] "MatrixDB" "NCI-PID_ProtMapper"
#> [59] "NRF2ome" "NetPath"
#> [61] "NetworKIN_KEA" "PhosphoNetworks"
#> [63] "PhosphoPoint" "PhosphoSite"
#> [65] "PhosphoSite_KEA" "PhosphoSite_MIMP"
#> [67] "PhosphoSite_ProtMapper" "PhosphoSite_noref"
#> [69] "ProtMapper" "REACH_ProtMapper"
#> [71] "RLIMS-P_ProtMapper" "Ramilowski2015"
#> [73] "Ramilowski2015_Baccin2019" "Reactome_LRdb"
#> [75] "Reactome_ProtMapper" "Reactome_SignaLink3"
#> [77] "SIGNOR" "SIGNOR_ProtMapper"
#> [79] "SPIKE" "SPIKE_LC"
#> [81] "STRING_talklr" "SignaLink3"
#> [83] "Sparser_ProtMapper" "TCRcuration_SignaLink3"
#> [85] "TRIP" "UniProt_LRdb"
#> [87] "Wang" "Wojtowicz2020"
#> [89] "connectomeDB2020" "dbPTM"
#> [91] "iPTMnet" "iTALK"
#> [93] "phosphoELM" "phosphoELM_KEA"
#> [95] "phosphoELM_MIMP" "scConnect"
#> [97] "talklr"
```